Surface-Coated Cutting Tool

ABSTRACT

A coating layer formed from an outermost layer and an inner layer disposed on a substrate surface of a surface coated cutting tool. The inner layer is formed from a periodic table group IVa, Va, VIa metal, Al, Si, B compound. The outermost layer is formed from aluminum nitride or aluminum carbonitride. The outermost layer has a chlorine content of more than 0 and no more than 0.5 atomic percent. The protective coating on the tool surface is made easier to form during cutting by further adding a predetermined amount of chlorine to the film formed from aluminum nitride, which provides thermal stability and lubricity. Lubricity can be increased by using this protective coating.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a U.S. national phase application under 35 U.S.C.§371 of International Patent Application No. PCT/JP2005/007180, filedApr. 13, 2005, and claims the benefit of Japanese Application No.2004-118340, filed Apr. 13, 2004, Japanese Application No. 2004-118341,filed Apr. 13, 2004, Japanese Application No. 2004-118346, filed Apr.13, 2004, and Japanese Application No. 2004-118348, filed Apr. 13, 2004,all of which are incorporated by reference herein. The InternationalApplication was published in Japanese on Oct. 27, 2005 as InternationalPublication No. WO 2005/099945 A1 under PCT Article 21(2).

TECHNICAL FIELD

The present invention relates to a cutting tool, such as a throw-awayinsert or drill, equipped with a coating layer on a substrate surface.

More specifically, the present invention relates to a surface-coatedcutting tool with superior lubricity that is suited for cutting steeland the like.

BACKGROUND ART

Examples of widely known cutting tools include throw-away inserts usedfor turning and milling as well as end mills generally used for sidemilling, beveling, and fluting various types of metals, and drills usedfor boring. These end mills and drills are formed with a section thatincludes a cutting section, known as the body, and a section known asthe shank that is mounted in a drive device. Examples of bodies include:solid bodies, where the body is formed integrally from a cutting sectionand a support that includes a flute for supporting the cutting sectionand allowing chips to be ejected; brazed bodies, where the cuttingsection is brazed to the support; and throw-away bodies, where thecutting section can be attached to and removed from the support.Conventionally, solid bodies are formed from high-speed tool steel orcemented carbide. Brazed bodies are formed by brazing a cutting sectionformed from a hard material such as cemented carbide to a support formedfrom high-speed tool steel.

In recent years, various cutting tool materials have been developed tomeet the demand for higher efficiency and precision in cutting. In theprocess of developing these materials, ceramic coating technology, inwhich a coating layer formed from ceramics is applied to the surface ofa tool substrate, has become a crucial technology in cutting tools. Forexample, the use of titanium-based ceramics, e.g., titanium carbide(TiC), titanium nitride (TiN), titanium carbonitride (Ti(C,N)), andoxide-based ceramics, e.g., alumina (Al₂O₃) and zirconia (ZrO₂) to formcoating layers for cutting tools used in high-speed, high-efficiencyoperations involving high speeds and high feeds is widely known.Japanese Laid-Open Patent Publication Number Hei 11-124672 describes athrow-away insert equipped with a coating layer with a defined X-raydiffraction index of orientation. This insert is used in high-speed,high-efficiency operations involving high speeds and high feeds. Inaddition to throw-away inserts, this type of ceramic coating technologyis also becoming widely used in solid and brazed tools that are oftenused in end mills and drills.

The inclusion of a ceramic coating on a cutting tool improves surfacehardness and heat resistance and allows the tool to handle high-speed,high-efficiency operations involving high speeds and high feeds. Inaddition to this type of high-speed, high-efficiency operation, inrecent years attention has been given to methods that protect theenvironment such as mist cutting, where the use of cutting oil isdrastically reduced, or dry cutting, where cutting oil is not used. Tohandle these types of operations, throw-away inserts equipped with acoating layer with superior welding resistance or a coating layer with achip sliding feature (see Japanese Laid-Open Patent Publication NumberHei 10-158861 and Japanese Laid-Open Patent Publication Number2003-225808), and a drill coated with a CrN film having lubricity(Japanese Laid-Open Patent Publication Number 2003-275911) have beenproposed. In addition, cutting tools equipped with an aluminum nitridecoating layer for improved heat dissipation and the like have beenproposed (see Japanese Examined Patent Publication Number Sho 59-27382;Japanese Patent Publication Number 2861113; Japanese Laid-Open PatentPublication Number 2002-273607; Japanese Laid-Open Patent PublicationNumber 2002-263933; Japanese Laid-Open Patent Publication Number2002-263941; Japanese Laid-Open Patent Publication Number 2003-19604;Japanese Laid-Open Patent Publication Number 2003-25112; and JapaneseExamined Patent Publication Number Sho 59-27302.

However, all of the conventional cutting tools described above haveinsufficient lubricity, especially for mist cutting and dry cutting, inwhich no cutting oil is used. This leads to reduced tool life. Thus,there is a need to improve lubricity so that tool life can be extended.With end mills and drills in particular, high lubricity is important forincreasing the ability of chips to be ejected out through the fluteformed on the body. High lubricity is also preferable for cuttingmaterials that tend to weld and for deep hole boring, where the abilityof chips to be ejected out is important.

SUMMARY OF THE INVENTION

The present invention provides a surface-coated cutting tool withimproved lubricity and extended tool life by defining the composition ofan outermost layer to contain predetermined elements so that lubricityis provided for the outermost layer, which makes initial contact withthe workpiece during cutting, and by defining the composition of theinner layer to improve wear resistance and fracturing resistance.

More specifically, the present invention provides a surface-coatedcutting tool equipped with a coating layer on a substrate surface. Thecoating layer is formed from an inner layer formed on a substrate and anoutermost layer formed over the inner layer. The outermost layer and theinner layer meet the following conditions.

<Inner Layer>

The inner layer is formed from a compound formed from a first elementand a second element, the first element being at least one elementselected from a group consisting of a periodic table group IVa, Va, VIametal, Al, Si, and B, and the second element being at least one elementselected from a group consisting of B, C, N, and O (except if the firstelement is B by itself, the second element is an element other than B).

<Outermost Layer>

The outermost layer is formed from aluminum nitride or aluminumcarbonitride. The outermost layer contains more than 0 and no more than0.5 atomic percent chlorine.

The present inventors investigated the interrelationships betweencoating layers and ways of improving coating layer properties in orderto extend tool life even when a cutting tool is used in usageenvironments that impose harsh conditions, e.g., in the case ofthrow-away inserts used for turning and the like, cutting operationsthat involve high temperatures for the cutting edge such as dry cutting,where no cutting oil is used, and intermittent cutting, and, in the caseof drills and end mills, cutting operations such as mist cutting, drycutting, boring, and cutting of workpieces that tend to easily weld. Asa result, it was found that tool life could be extended efficiently byusing a coating film with superior lubricity as the outermost layer andforming the inner layer with films having a predetermined composition.More specifically, by forming the outermost layer from a film formedfrom aluminum nitride containing a predetermined amount of chlorine asdescribed above, lubricity can be provided even in cutting operationssuch as dry cutting, intermittent cutting, and boring. As a result,welding resistance is improved and the coating layer can be preventedfrom peeling. In the case of throw-away inserts used in the turning andthe like the superior lubricity reduces the cutting force received bythe tool and, also, fracturing resistance and wear resistance can beimproved by forming the inner layer from films having a predeterminedcomposition while using a film with superior lubricity, “shredding” ofthe workpiece surface after cutting due to contact with the cutting toolis reduced, thus providing high-quality, high-precision workpieces.Furthermore, in the case of drills and end mills the superior lubricityreduces the cutting force received by the tool and improves ejection ofchips and breakage resistance, while the use of predeterminedcompositions for the films in the inner layer improves wear resistance,chipping resistance, and fracturing resistance. Further, using a coatinglayer with superior lubricity, the product quality can be improved,e.g., the roundess of holes can be improved, thus providing high-qualityand high-precision workpiece products. The present invention was definedbased on these observations.

The improvement in tool life described above is currently believed to befor the following reasons. The aluminum nitride film provides thermalstability and lubricity. Also, when an aluminum nitride film contains apredetermined amount of chlorine, in the case of cutting operations withthrow-away inserts that tend to raise the temperature of the cuttingedge, e.g., dry cutting and high-speed and high-feed cutting, aprotective film is easy to form on the tool surface when the cuttingedge reaches a high temperature of approximately 900 deg C. duringcutting. This protective film can improve lubricity and is believed toimprove the welding resistance of the tool. Also, by forming films frompredetermined compositions for the inner layer, reduction of wearresistance can be avoided, thus making it possible to provide a toolwith both superior lubricity and superior wear resistance. With drillsand end mills, the use of an aluminum nitride film containing apredetermined amount of chlorine is believed to reduce the frictioncoefficient between chips and areas associated with cutting(specifically, the tool surfaces at the cutting edge and the flutes). Asa result, at the area around the cutting edge, the work needed togenerate chips is reduced and the chips are more easily ejected, leadingto adequate tool life for cutting operations such as dry cutting, deepboring, and cutting of easily welded workpieces, while the quality andcutting precision of the workpiece is also improved. It is also believedthat by including a predetermined amount of chlorine in the outermostlayer, in addition to the friction coefficient being reduced, theformation of a protective film on the tool surface becomes easier incutting operations that tend to result in high temperature and highpressure for the cutting edge, e.g., dry cutting and deep boring. Thisprotective film is believed to improve the lubricity of the tool so thatthe welding resistance of the tool is improved. Furthermore, it isbelieved that by forming the inner layer from films having predeterminedcompositions, it is possible to avoid reducing wear resistance so that atool with both superior lubricity and wear resistance can be provided.The present invention is described in further detail below.

(Coating Layer)

<Outermost Layer>

In the present invention, the outermost layer, which makes initialcontact with the workpiece when performing a cutting operation, isformed from an aluminum compound such as aluminum nitride or aluminumcarbonitride. Then, in the present invention, chlorine is included inthis film formed from aluminum nitride. More specifically, more than 0and no more than 0.5 atomic percent of chlorine is included in theoutermost layer. The inclusion of no more than 0.5 atomic percent ofchlorine in the outermost layer makes it possible for a protective filmto form in high-temperature cutting environments, thus improvinglubricity. If the chlorine content exceeds 0.5 atomic percent, the filmforming the outermost layer can peel easily. If there is no chlorine,the protective film described above does not form. It is preferable forthe chlorine content to be at least 0.07 atomic percent and no more than0.3 atomic percent. If a chemical vapor deposition (CVD) technique suchas thermal CVD or plasma CVD is used to form the aluminum nitride filmcontaining more than 0 and no more than 0.5 atomic percent of chlorinein the outermost layer, the reaction gas can be a gas containingchlorine such as hydrogen chloride (HCl). In this case, the hydrogenchloride content can be more than 0 and less than 5.0 percent by volume,and more specifically no more than 1.0 percent by volume, where theentire reaction gas is defined as 100 percent by volume. If a physicalvapor deposition (PVD) technique such as arc ion plating or magnetronsputtering is used to form the aluminum nitride film, chlorine ions canbe implanted after the film is formed using ion implantation. Thechlorine content in the outermost layer can be adjusted by controllingthe amount of implantation as appropriate.

The outermost layer can further include oxygen. More specifically, inaddition to aluminum nitride and aluminum carbonitride, the outermostlayer can be formed as an aluminum oxynitride or an aluminum carbonoxynitride film. The inclusion of oxygen makes the protective filmeasier to form.

With this type of outermost layer, it is preferable for the filmthickness to be no more than ½ the total film thickness of the innerlayer described later. This allows the coating layer to provide a goodbalance between wear resistance and lubricity, e.g., for forming theprotective film. If the thickness exceeds ½, the outermost layer becomestoo thick, so that while superior lubricity is provided, wear tends totake place, possibly leading to shorter tool life. More specifically, ifthe cutting tool of the present invention is to be a throw-away insert,it is preferable for the film thickness of the outermost layer to be atleast 0.03 microns and no more than 10 microns. If the cutting tool ofthe present invention is to be a drill or an end mill, it is preferablefor the thickness to be at least 0.03 microns and no more than 8microns. If the thickness is less than 0.03 microns, obtaining adequatelubricity becomes difficult. If the thickness exceeds 10 microns or 8microns, the outermost layer becomes thicker than the inner layer,tending to reduce wear resistance as described above. Film thickness canbe measured, for example, by cutting the cutting tool, e.g., an insertor drill with a coating layer, and observing the cross-section under anSEM (scanning electron microscope).

At the outermost layer, it is preferable for the surface roughness atareas on the outermost layer near the ridge line of the cutting edge atareas that come into contact with the workpiece to have an Rmax relativeto a reference length of 5 microns of no more than 1.3 microns, wherethe roughness is measured by observing a cross-section of the cuttingtool. Based on studies by the inventors, it was found that when thesurface roughness of these contact areas of the outermost layers has anRmax that exceeds 1.3 microns, welding tends to take place with theworkpiece, making it difficult to provide the advantages of lubricity.The surface roughness is measured by cutting the substrate after theoutermost layer is formed, performing lapping on the cross-section,observing the roughness on the film surface using a metallurgicalmicroscope or an electron microscope, and determining the maximumsurface roughness (Rmax) within a reference length of 5 microns, thuseliminating macroscopic swelling and the like. Also, this surfaceroughness can be controlled to some degree through film formingconditions. For example, crystal structure becomes more coarse at higherfilm forming temperatures, and by extension there is more surfaceroughness on the film surface. Thus, film forming temperature can belowered to reduce surface roughness. Thus, Rmax can be set to no morethan 1.3 microns when the film is formed without requiring specialtreatment after film formation. However, it is also possible to changesurface roughness after film formation, e.g., by polishing with a buff,brush, barrel, elastic grindstone or the like, or by performing surfacereforming through microblasting, shot peening, or ion-beam radiation.

<Inner Layer>

The inner layer is formed from a compound formed from a first elementand a second element, the first element being at least one elementselected from a group consisting of a periodic table group IVa, Va, VIametal, Al, Si, and B, and the second element being at least one elementselected from a group consisting of B, C, N, and O (except if the firstelement is B by itself, the second element is an element other than B).More specifically, films formed from compounds containing Ti such asTiCN, TiN, TiBN, and TiCNO and films formed from oxides such as Al₂O₃and ZrO₂ provide superior wear resistance and are preferable. Also,since TiN has good adhesion with the substrate, it is preferable for itto be used as the innermost layer. The inner layer can be formed from asingle film or can be formed from multiple films. If the inner layer isformed from multiple films, the films should have different compositionsor structures. The inner layer can be formed either through CVD, e.g.,thermal CVD or plasma CVD, or through PVD, e.g., arc ion plating ormagnetron sputtering. The inner layer can be formed using widely knownconditions.

By forming the inner layer with a Ti compound film as described above,superior wear resistance is provided. More specifically, a film formedfrom TiCN is suitable, and in particular it is preferable to use a TiCNfilm with columnar structure. Furthermore, it is more preferable to usea film formed from TiCN that has a columnar structure with an aspectratio of at least 3, where an index of orientation (orientationintensity coefficient) TC(220), TC(311), or TC(422) of a crystal face(220), crystal face (311), or crystal face (422) respectively is themaximum index of orientation. By using a TiCN film with a structurehaving a predetermined shape and with a crystal face having apredetermined orientation, improved wear resistance and extended toollife is provided even in harsh cutting environments, e.g., where thecutting edge reaches high temperatures.

The columnar structure is defined to have an aspect ratio of at least 3because if the aspect ratio is less than 3, there tends to be reducedwear resistance under high-temperature cutting conditions. The desiredwear resistance is difficult to obtain with a granular structure.

A columnar structure can be formed, for example, if the film is formedusing CVD, by using a raw gas that is an organic carbonitride thatallows a columnar structure to be easily formed such as CH₃CN and bycontrolling the reaction atmosphere temperature (at least 800 deg C. andno more than 950 deg C.) and pressure (at least 4.0 kPa and no more than80 kPa). If a gas other than an organic carbonitride is used, the filmgrowth rate can be increased, the film forming temperature can beincreased, the concentration of the raw gas can be increased, or thelike. An aspect ratio of at least 3 can be achieved, for example, byreducing the average grain size of the crystal (preferably at least 0.05microns and no more than 1.5 microns) and growing the film structurewith a columnar structure. This can be done, for example, byappropriately adjusting the TiCN film forming conditions (film formingtemperature, film forming pressure, gas composition, gas flow rate, gasflow volume, and the like). It is also possible to appropriately adjustthe surface state of the substrate below or directly below the TiCN filmor the surface state of the coating film located below or directly belowthe TiCN film. More specifically, it is possible, for example, tocontrol the surface roughness of the substrate surface to have an Rmax(5 microns reference length) of at least 0.05 microns and no more than1.5 microns and to form the TiCN film by appropriately changing the filmforming conditions. Alternatively, it is possible to control the surfaceroughness, chemical state, or grain diameter (preferably at least 0.01microns and no more than 1.0 microns), or the like of a film, and toform the TiCN film on top of this film with the film forming conditionsadjusted appropriately.

The aspect ratio described above can, for example, be measured in thefollowing manner. A specular polish is applied to a cross-section of thecoating layer and the grain boundary of the structure of the columnarstructure TiCN film is etched. Then, treating the widths of individualcrystals parallel to the substrate at a position corresponding to ½ thefilm thickness of the TiCN film as grain sizes, the grain diameters ofthe crystals are measured and an average is calculated (the average isused as the average grain size). The proportion of the average grainsize relative to the film thickness is calculated by dividing the filmthickness by the obtained average grain size, and this value can be usedas the aspect ratio.

This TiCN film with a predetermined aspect ratio has the predeterminedcrystal orientations for the crystal faces as described. The index oforientation TC is defined as follows. $\begin{matrix}{{{TC}\left( {{hk}\quad 1} \right)} = {\frac{I\left( {{hk}\quad 1} \right)}{I_{0}\left( {{hk}\quad 1} \right)}\left( {\frac{1}{8}{\sum\frac{I\left( {{hk}\quad 1} \right)}{I_{0}\left( {{hk}\quad 1} \right)}}} \right)^{- 1}}} & {{Equation}\quad 1}\end{matrix}$I(hk1): measured diffraction intensity of the (hk1) face; I₀(hk1):average powder diffraction intensity based on JCPDS file of the carbideof the metal forming the (hk1) face and the nitride of the same metal;(hk1): the eight faces (111), (200), (220), (311), (331), (420), (422),(511)

Making one of the indices of orientation (orientation intensitycoefficient) TC(311), TC(220), or TC(422) be the maximum can be achievedby appropriately adjusting film forming conditions (film formingtemperature, film forming pressure, gas composition, gas flow rate, gasflow volume, and the like) for the TiCN film. It is also possible toappropriately adjust the surface state of the substrate below ordirectly below the TiCN film or the surface state of the film below ordirectly below the TiCN film. More specifically, for example, the TiCNfilm can be formed on a substrate that has been prepared with a surfaceroughness Rmax (5 microns reference length) of at least 0.05 microns andno more than 1.5 microns, with the film forming conditions appropriatelyadjusted. Alternatively, for one of the films, the surface roughness,the chemical state of the grains, the grain size, or the like can becontrolled, and then the TiCN film can be formed on top of this filmwith appropriately adjusted film forming conditions.

It is preferable for the diffraction intensity to be measured for a flatsection (smooth section) of the substrate cross-section so that surfaceindentations on the substrate do not create reflections. Also, the JCPDSfile (Powder Diffraction File Published by JCPDS International Centerfor Diffraction Data) does not provide identification of X-raydiffraction intensity for carbonitrides of periodic table IVa, Va, VIagroup metals. Thus, identification of diffraction intensity for the TiCNfilm, which is one of these carbonitrides, can be obtained by comparingdiffraction data for the carbide of titanium (Ti), which is thecorresponding metal, diffraction data for the nitride of the same, andthe measured diffraction data for the TiCN carbonitride. Based on this,the face indices can be estimated, and the diffraction intensities forthe face indices can be obtained.

If the inner layer is formed from multiple films, at least one of thefilms can be the TiCN film with the predetermined aspect ratio and thelike as described above, and the other films can be compound filmsformed from a first element and a second element as described above. Theinner layer can, thus, be formed from this TiCN film and this compoundfilm. The compound film can be a film having a composition differentfrom that of the TiCN film or can be a TiCN film having a structure ororientation that is different from this TiCN film. The TiCN film can bea single film or can be multiple films. Either the compound film or theTiCN film can be positioned closer toward the substrate. In other words,the structure, starting from the substrate side, can be the TiCN film,the compound film, the outermost layer, or can be the compound film, theTiCN film, and the outermost layer.

If the cutting tool of the present invention is to be a throw-awayinsert, it is preferable for the film thickness of the coating layer,formed from the outermost layer and the inner layer, to be at least 0.1microns and no more than 30.0 microns. If the film thickness of theentire coating layer is less than 0.1 microns, improved wear resistancebecomes difficult to obtain. If the thickness exceeds 30.0 microns, thethicker coating layer improves wear resistance, but the increasedhardness tends to increase fractures, leading to shortened tool life andmaking stable cutting difficult. If the cutting tool of the presentinvention is to be a drill or end mill, it is preferable for the filmthickness of the coating layer, formed from the outermost layer and theinner layer, to be at least 0.1 microns and no more than 24 microns. Ifthe film thickness of the entire coating layer is less than 0.1 microns,improved wear resistance tends to become difficult to obtain. If thethickness exceeds 24 microns, the thicker coating layer improves wearresistance, but the peeling resistance and fracture resistance isreduced. This leads to frequent chipping, making stable cuttingdifficult.

It is preferable for the outermost layer described above to be formedwith a film hardness lower than that of at least one of the filmsforming the inner layer. In other words, it is preferable for the innerlayer to include a film having a film hardness that is greater than thatof the outermost layer. With an outermost layer having a low filmhardness, it is possible to prevent fractures that occur when the toolinitially engages with the workpiece or in intermittent cutting. Thismakes it possible to provide stable cutting. In addition to changingfilm composition, film hardness can be adjusted by controlling the filmstructure through the film forming conditions. Given the same filmcomposition, film hardness tends to be greater when the film structureis finer. The hardness of the films can be measured by cutting thecutting tool with the coating layer, e.g., the insert or the drill, andmeasuring the hardness at the cross-section.

The coating layer coats at least the areas of the substrate surfaceassociated with cutting. The coating layer can cover the entiresubstrate surface. In the case of a throw-away insert, for example, theareas associated with cutting are the ridge line of the cutting edge,the rake face, and the flank face. In the case of an end mill or adrill, the area associated with cutting is what is generally known asthe body, formed from a cutting section and a support. FIG. 1 (A) is asimplified front-view drawing of an end mill. FIG. 1 (B) is a simplifiedfront-view drawing of a drill. More specifically, in the case of an endmill, the areas associated with cutting are, as shown in FIG. 1 (A), acutting edge section formed from an end surface (an end cutting edge 1)and a side surface (a peripheral cutting edge 2) associated with theactual cutting and a flute 3 that comes into contact with chips. Insteadof forming the coating layer just on the body, it is also possible tohave the coating layer extend from a body 4, where the flute is formedfrom the end surface, to the section referred to as a shank 5 that ismounted in the driving device. In the case of a drill, the areasassociated with cutting are the tip 6 associated with the actual cuttingand a groove (flute) 7 that comes into contact with the chips. With adrill as well, it is possible instead of forming the coating layer onlyon a body 8 to extend the coating layer from the body 8, where the endand the flute are formed, to a shank 9 that is mounted in the drivingdevice. For the areas where the coating layer is not formed, appropriatemasking can be applied during film forming or polishing or the like canbe performed after the film has been formed to remove the film.

Of course, after the coating film formed from the outermost layer andthe inner layer are formed on the substrate surface, it is possible, asin the conventional technology, to apply surface treatment such aspolishing or applying a laser to the ridge line of the cutting edge.With the cutting tool of the present invention, this type of surfacetreatment does not significantly reduce the characteristics of thecoating layer.

(Substrate)

It is preferable for the substrate of the present invention, especiallythe areas of the substrate associated with cutting, to be formed from aWC-based cemented carbide, cermet, high-speed steel, ceramic, a cubicboron nitride sintered body, or a silicon nitride sintered body. Morespecifically, if the cutting tool of the present invention is a drill oran end mill, it is preferable for at least the areas of the substrateassociated with cutting to be formed from a WC-based cemented carbide,cermet, high-speed steel, or a cubic boron nitride sintered body. If asubstrate formed from a WC-based cemented carbide or cermet is used, theadvantages of the present invention are provided even if, on thesubstrate surface or the areas of the substrate surface associated withcutting, there is a reformed surface layer such as a “β-free layer” inwhich non-WC hardness phase has been removed, a binder-rich layer thatis rich in binder and from which the hardness phase has been removed, ora hardened surface layer in which the binder phase has been removed.

The present invention can be implemented for various types of cuttingtools such as drills, end mills, replaceable milling inserts,replaceable turning inserts, metal saws, gear cutting tools, reamers,and taps. In particular, the present invention is suited for throw-awayinserts, drills, and end mills. For drills and end mills, the presentinvention is used for solid drills and end mills, where the cuttingsection and the support are sintered or formed integrally, or for brazeddrills and end mills, where the cutting section is brazed to thesupport, rather than throw-away (replaceable cutting edge) tools, wherethe cutting section and the support can be attached or removed. In thecase of brazed tools, it is preferable for the coating layer to beformed using PVD, which has a relatively low film-forming temperature.For solid tools, the coating layer can be formed using PVD or CVD, whichhas a relatively high film-forming temperature.

The surface-coated cutting tool of the present invention as describedabove is equipped with a predetermined coating layer. As a result,superior lubricity is provided as well as superior wear resistance,peeling resistance, fracture resistance, and breakage resistance. Thus,superior cutting properties and extended tool life are provided evenunder usage environments involving harsh cutting conditions such as drycutting, deep boring, cutting of workpieces that tend to weld easily,and other cutting operations such as high-speed, high-efficiency cuttingwhere the cutting edge is exposed to high temperatures.

In particular, since the surface-coated cutting tool of the presentinvention is equipped with a predetermined TiCN film in the inner layer,both superior lubricity and superior wear resistance are provided, andtool life is extended with superior cutting characteristics even underthe harsh usage environments described above.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 (A) is a simplified front-view drawing of an end mill. FIG. 1 (B)is a simplified front-view drawing of a drill.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be described.

FIRST EXAMPLE

Using a throw-away insert for turning as an example, the presentinvention will be described more specifically below.

TEST EXAMPLE 1-1

A powder with 86 percent by mass of WC, 8.0 percent by mass of Co, 2.0percent by mass of TiC, 2.0 percent by mass of NbC, and 2.0 percent bymass of ZrC was prepared. The powder was wet mixed for 72 hours with aball mill, dried, and then pressed into a green compact with a breakerstructure. This green compact was heated for 1 hour in a vacuumatmosphere at 1420 deg C. in a sintering furnace, resulting in asintered body. SiC brush honing and beveling were performed at the ridgeline of the cutting edge of the obtained sintered body, resulting in anISO SNMG120408 throw-away insert formed from WC-based cemented carbide.

A coating layer was formed on the substrate surface using thermal CVD, achemical vapor deposition technique. In this test, starting from thesubstrate side, an inner layer was formed from TiN(0.5), TiCN(6),TiBN(0.5), κ-Al₂O₃(2) and an outermost layer was formed from AlN(3). Thenumbers in parentheses indicate film thickness in microns. Table 1 showsan example of film forming conditions for each film. Specifically, thecomposition of the reaction gas (percent by volume), the pressureapplied when forming the film (kPa), and the film forming temperature(deg C) are shown. Film thickness was controlled by controlling the filmforming time. Test samples in which the AlN film at the outermost layerhave different chlorine contents were prepared by varying the filmforming conditions as shown in Table 1. Table 2 shows chlorine contentat the outermost layer. Specifically, samples with more than 0 and nomore than 0.5 atomic percent of chlorine, samples with more than 0.5atomic percent of chlorine, and samples with no chlorine were prepared.Chlorine content was varied as shown in Table 1 by varying theproportion of hydrogen chloride (HCl) in the reaction gas. Also,depending on the amount of hydrogen chloride, the film forming pressureand the film forming temperature were varied as appropriate.Furthermore, the surface roughness at sites on the outermost layer nearthe ridge line of the cutting edge at areas that come into contact withthe workpiece were studied for test samples containing more than 0 andno more than 0.5 atomic percent of chlorine in the outermost layer.Observation of the tool cross-sections showed that the Rmax for areference length of 5 microns was no more than 1.3 microns for allsamples. More specifically, the Rmax was 0.6 microns for Test Sample1-2, for example. The chlorine content was measured using XPS (X-rayPhotoelectron Spectroscopy), but composition can also be studied usingmicro-EDX (Energy Dispersive X-ray Spectroscopy) combined with atransmission electron microscope or using SIMS (Secondary Ion MassSpectrometry). Also, the Knoop hardness for each of the layers in thetest samples was studied, and it was found that in all cases theoutermost AlN film was softer than the inner TiCN film layer. TABLE 1Pres- Temper- Coating Reaction gas composition sure ature layer (vol %)(kPa) (deg C.) AlN *¹ AlCl₃: 1.0-5.0%, NH₃: 0.1-5.0%, 4.0-80 750-980 N₂:20-50%, HCl: 0.01-1.0%, H₂: rest AlCN *¹ AlCl₃: 1.0-5.0%, NH₃: 0.1-5.0%,4.0-80 750-980 N₂: 20-50%, CH₄: 0.5-5.0%, HCl: 0.01-1.0%, H₂: rest AlON*¹ AlCl₃: 1.0-5.0%, NH₃: 0.1-5.0%, 4.0-80 750-980 N₂: 20-50%, CO₂:0.2-3.0%, HCl: 0.01-1.0%, H₂: rest AlN *² AlCl₃: 1.5%, NH₃: 1.0%, 5.01000 N₂: 40%, H₂: rest AlN *³ AlCl₃: 1.5%, NH₃: 3.0%, 13.3 950 N₂: 40%,HCl: 5.0%, H₂: rest AlON *² AlCl₃: 1.5%, NH₃: 6.0%, 6.8 1100 N₂: 40%,CO₂: 1.0%, H₂: rest TiN TiCl₄: 2.0%, N₂: 25%, H₂: rest 13.3 950 TiCTiCl₄: 2.0%, CN₄: 5%, H₂: rest 13.3 1050 TiCN TiCl₄: 2.0%, CH₃CN: 0.6%,6.7-80 800-950 N₂: 20%, H₂: rest ZrCN ZrCl₄: 1.0%, CH₃CN: 0.6%, 6.7 890N₂: 35%, H₂: rest TiZrCN TiCl₄: 1.5%, ZrCl₄: 1.0%, 6.7 975 CH₃CN: 1.0%,N₂: 45%, H₂: rest TiCNO TiCl₄: 2.0%, CO₂: 2.5%, 6.7 975 N₂: 8%, H₂: restTiBN TiCl₄: 2.0%, BCl₃: 5.0%, 13.3 950 N₂: 5.0%, H₂: rest HfCN HfCl₄:1.0%, CH₃CN: 1.2%, 6.7 1025 N₂: 40%, H₂: rest α Al₂O₃ AlCl₃: 2.0%, H₂S:0.3%, 6.7 1050 CO₂: 5.0%, H₂: rest κ Al₂O₃ AlCl₃: 2.0%, CO₂: 5.0%, 6.71000 CO: 0.5%, H₂: rest ZrO₂ ZrCl₄: 2.0%, CO₂: 7.0%, 6.7 1050 H₂: restAl₂O₃—ZrO₂ AlCl₃: 1.5%, ZrCl₄: 0.3%, 13.3 1070 CO₂: 9.0%, H₂: rest*¹ Chlorine content is more than 0 and no more than 0.5 atomic percent*² No chlorine*³ Chlorine content is more than 0.5 atomic percent

TABLE 2 Test Sample Outermost Chlorine content No. layer (atomic %) 1-1AlN *¹ 0.02 1-2 AlN *¹ 0.15 1-3 AlN *¹ 0.49 1-4 AlN *² 0 1-5 AlN *³ 0.90

Using the surface-coated throw-away inserts with the outermost layers asshown in Table 2, cutting operations were performed using the cuttingconditions shown in Table 3. The cutting time involved in reaching thetool life was measured. In a peeling resistance test, cutting operationswere repeated, with the end of tool life defined to be when flank facewear due to film peeling was at least 0.3 mm. In a fracturing resistancetest, intermittent cutting was performed, with the end of tool lifedefined to be when a fracture occurred. The results of the tests areshown in Table 4. TABLE 3 Peeling resistance test Fracture resistancetest Workpiece S15C rod S45C fluted rod 3-sec repetition test Speed V =300 m/min V = 260 m/min Feed f = 0.3 mm/rev. f = 0.2 mm/rev. Cuttingdepth d = 1.0 mm d = 1.5 mm Cutting oil None None

TABLE 4 Test sample Cutting time (min) No. Peeling resistance testFracture resistance test 1-1 40 23 1-2 63 30 1-3 52 21 1-4 10 7 1-5 9 4

Based on the results, in the Test Samples 1-1 through 1-3, which havealuminum nitride layers with more than 0 and not more than 0.5 atomicpercent of chlorine on the outermost layer as shown in Table 4, superiorlubricity and improved welding resistance was observed even inenvironments where the cutting edge reaches high temperature, such as indry cutting and intermittent cutting. This provided superior peelingresistance as well as superior fracturing resistance due to reducedcutting force. Also, these Test Samples 1-1-1-3 showed reduced wear,indicating superior wear resistance. Based on these factors, it can beseen that the Test Samples 1-1-1-3 provide longer cutting times andextended tool life.

TEST EXAMPLE 1-2

A cemented carbide substrate similar to the one used in the Test Example1-1 was prepared. Thermal CVD was performed on the surface of theobtained substrate to form a coating layer with the film formingconditions (gas composition, pressure, temperature) shown in Table 1.Table 5 shows the composition, film thicknesses, and film thickness ofthe entire coating layer (total film thickness). In Table 5, the filmsare indicated sequentially as the first film, the second film, and thelike starting from the film closest to the substrate. TABLE 5 Test Totalsam- First film Second film Third film Fourth film Fifth film Sixth filmThick- Cutting ple Thick- Thick- Thick- Thick- Thick- Thick- ness timeNo. Type ness Type ness Type ness Type ness Type ness Type ness μm (min)2-1  TiCN 5.0 AlN*¹ 2.0 7.0 20 2-2  TiN 0.5 ZrCN 7.0 AlN*¹ 0.5 8.0 312-3  TiN 1.0 TiCN 4.5 TiC 1.5 TiCNO 1.0 κ Al₂O₃ 3.0 AlCN*¹ 5.0 16.0 352-4  TiN 0.3 TiCN 6.5 TiBN 0.5 κ Al₂O₃ 1.5 TiN 0.3 AlN*¹ 3.0 12.1 272-5  TiN 0.5 TiCN 20.0 Al₂O₃— 5.0 AlN*¹ 2.0 27.5 37 ZrO₂ 2-6  TiCN 3.0TiZrCN 5.0 ZrO₂ 2.3 Al₂O₃— 2.5 AlON*¹ 1.7 14.5 28 ZrO₂ 2-7  TiCN 3.2 TiN0.5 HfCN 4.3 AlCN*¹ 2.5 10.5 21 2-8  TiN 0.5 TiBN 1.3 α Al₂O₃ 5.0 AlN*¹0.05 6.85 25 2-9  HfCN 3.5 α Al₂O₃ 1.5 TiCNO 2.3 TiCN 6.5 TiN 0.7 AlCN*¹0.7 15.2 30 2-10 TiN 5.0 TiZrCN 14.0 AlCN*¹ 9.0 28 32 2-11 TiN 0.5 TiCN4.5 AlCN*¹ 0.5 AlN*¹ 0.5 6.0 23 2-12 TiN 0.5 TiCNO 2.0 TiCN 6.0 TiBN 0.5κ Al₂O₃ 1.5 AlCN*¹ 0.7 11.2 25 2-13 HfCN 4.0 TiN 1.0 5.0 4 2-14 TiN 0.5TiCN 5.0 TiCNO 0.5 ZrO₂ 2.0 TiCN 0.1 TiN 2.0 10.1 6 2-15 TiN 0.5 AlON*¹2.0 α Al₂O₃ 3.0 TiN 1.5 7.0 6 2-16 ZrCN 0.07 AlN*¹ 0.02 0.09 8 2-17 TiN0.5 ZrCN 40 AlN*¹ 0.02 4.52 11 2-18 TiN 0.5 TiCN 3.0 TiCNO 11.0 α Al₂O₃3.5 Al₂O₃— 7.0 AlCN*¹ 10.0 35.0 7 ZrO₂ 2-19 TiCN 4.0 TiBN 2.0 ZrO₂ 2.0AlCN*¹ 8.0 16.0 13 2-20 TiN 1.0 ZrCN 4.0 AlON*² 1.3 6.3 5 2-21 AlN*¹ 5.05.0 3 2-22 TiN 3.0 AlCN*¹ 1.0 4.0 11 2-23 TiZrCN 10.0 AlCN*¹ 4.0 14.0 10

Repeated cutting was performed under the cutting conditions shown belowusing the surface-coated throw-away inserts with the coating layersshown in Table 5. The cutting time involved in reaching the tool lifewas measured. The end of tool life was defined to be when flank facewear was at least 0.3 mm. Table 5 shows the results from the test aswell.

Workpiece: 15-second repeated wear resistance test with SCM435 round rod

Speed: V=180 m/min

Feed: f=0.2 mm/rev.

Depth of cut: d=1.5 mm

Cutting oil: none

As a result, it was found as shown in Table 5 that, compared to theother test samples, Test Samples 2-1-2-12, 2-16-2-19, 2-22, and 2-23,which had an aluminum nitride film containing a predetermined amount ofchlorine as the outermost layer and films with predeterminedcompositions as the inner layers, provided superior lubricity andsuperior wear resistance.

Also, the results shown in Table 5 indicate that it is preferable forthe outermost layer to be at least 0.03 microns and for the total filmthickness to be at least 0.1 microns and no more than 30 microns.Furthermore, it can be seen that it is preferable for the outermostlayer to have no more than ½ the total thickness of the inner layer.

The inserts from the test sample 2-1-2-23 were all cut and the surfaceroughness relative to a 5 micron reference length was measured for thearea of the outermost layer near the ridge line of the cutting edge thatcomes into contact with the workpiece. As a result, it was found thatRmax was no more than 1.3 microns for all inserts except the Test Sample2-23, while the Rmax of the Test Sample 2-23 was 1.7 microns. For theTest Sample 2-23, a #1500 diamond paste was used to polish the area ofthe outermost layer near the ridge line of the cutting edge that comesinto contact with the workpiece. When the method described above wasused to measure surface roughness after polishing, Rmax was 0.52microns. When a cutting test was performed under the same cuttingconditions using the polished insert, the tool life was 22 min. This isbelieved to be caused by a reduction in the cutting force resulting fromless roughness at the area of the outermost layer near the ridge line ofthe cutting edge that comes into contact with the workpiece. When thesurface roughness of the Test Sample 2-3 was measured as describedabove, the Rmax was 0.76 microns, but when the cutting edge was polishedin the same manner, the tool life after another cutting operation wasfound to be significantly improved, at 45 min.

Furthermore, a coating film was formed on the Test Sample 2-22 makingthe film hardness of the inner layer lower than that of the outermostlayer. Then, the hardnesses of the films forming the coating layers ofthe Test Samples 2-1-2-20, 2-22, and 2-23 were measured. The filmhardness of the outermost layer was lower than that of at least one filmof the inner layer for all the inserts, with the exception of TestSample 2-22. With Test Sample 2-22, the film hardness of the outermostlayer was higher than that of the inner layer. Based on this, it isbelieved that the cutting efficiency of Test Sample 2-22 was reducedcompared to Test Samples 2-1-2-12.

TEST EXAMPLE 1-2′

Surface-coated inserts similar to those of the Test Samples 2-1-2-23were prepared and cutting tests were performed under the cuttingconditions described below. Crater wear (area: mm²) was then measuredfor a predetermined cutting length (500 m).

Workpiece: S50C

Speed: V=250 m/min

Feed: f=0.3 mm/rev.

Depth of cut: d=1.5 mm

Cutting oil: none

The results showed that the Test Samples 2-1-2-12, 2-16-2-19, 2-22, and2-23 had less crater wear compared to the other samples. For example,the results for the Test Samples 2-4, 2-5, and 2-6 were 0.45 mm², 0.39mm², and 0.44 mm², respectively.

TEST EXAMPLE 1-3

Surface-coated inserts were prepared using the substrate described belowwith a widely known PVD method used to form a coating layer having acomposition similar to that of the Test Samples 2-2, 2-13 from Table 5.For the insert with a coating layer having a composition similar to thatof the Test Sample 2-2, the surface-coated insert was formed by addingchlorine to the outermost layer using ion implantation after the coatinglayer was formed. Cutting tests with cutting conditions similar to thoseof Test Example 1-2 were performed using these surface-coated inserts.The test samples formed with the coating layer from the Test Sample 2-2all had a chlorine content of 0.2 atomic percent on the outermost layer.

1. JIS standard: P20 cermet cutting insert (T1200A, Sumitomo ElectricHardmetal Corp. Ltd.)

2. Ceramic cutting insert (W80, Sumitomo Electric Hardmetal Corp. Ltd.)

3. Silicon nitride cutting insert (NS260, Sumitomo Electric HardmetalCorp. Ltd.)

4. Cubic boron nitride cutting insert (BN250, Sumitomo ElectricHardmetal Corp. Ltd.)

The results showed that all the inserts with the coating layer havingthe composition from Test Sample 2-2 provided a tool life of at leasttwice that of conventional inserts with the coating layer having thecomposition from Test Sample 2-13.

TEST EXAMPLE 1-4

A powder with 86 percent by mass of WC, 8.0 percent by mass of Co, 2.0percent by mass of TiC, 2.0 percent by mass of NbC, and 2.0 percent bymass of ZrC was prepared. The powder was wet mixed for 72 hours with aball mill, dried, and then pressed into a green compact with a breakerstructure. This green compact was heated for 1 hour in a vacuumatmosphere at 1420 deg C. in a sintering furnace, resulting in asintered body. SiC brush honing and beveling were performed at the ridgeline of the cutting edge of the obtained sintered body, resulting in anISO SNMG120408 throw-away insert formed from WC-based cemented carbide.

A coating layer was formed on the substrate surface using thermal CVD, achemical vapor deposition technique. In this test, starting from thesubstrate side an inner layer was formed from TiN(0.5), columnarstructure TiCN(6), TiBN(0.5), κ-Al₂O₃(2) and an outermost layer wasformed from AlN(3). The numbers in parentheses indicate film thicknessin microns. Table 6 shows an example of film forming conditions for eachfilm. Specifically, the composition of the reaction gas (percent byvolume), the pressure applied when forming the film (kPa), and the filmforming temperature (deg C) are shown. Film thickness was controlled bycontrolling the film forming time. In this test, the TiCN film was grownso that it has a columnar structure with an aspect ratio of 4.2 and sothat the (311) plane has the maximum index of orientation TC. Morespecifically, the TiN film formation conditions (gas composition,pressure, temperature) were set up so that the reaction gas was CH₃CN,the temperature was 900 deg C., the pressure was 8 kPa, and the surfaceroughness Rmax (5 microns reference length) of the TiN film formed belowthe TiCN film was 0.1 microns. Then, the film forming conditions werevaried as shown in Table 6 to form AlN films on the outermost layer withdifferent chlorine content. Table 7 shows chlorine content on theoutermost layer. More specifically, test samples were prepared with morethan 0 and no more than 0.5 atomic percent chlorine on the outermostlayer, more than 0.5 atomic percent chlorine, and no chlorine. Thechlorine content was varied by varying the proportion of hydrogenchlorine (HCl) in the reaction gas as shown in Table 6. Also, dependingon the amount of hydrogen chloride, the film forming pressure and thefilm forming temperature were varied as appropriate. Furthermore, thesurface roughness at sites on the outermost layer near the ridge line ofthe cutting edge at areas that come into contact with the workpiece werestudied for test samples containing more than 0 and no more than 0.5atomic percent of chlorine in the outermost layer. Observation of thetool cross-sections showed that the Rmax for a reference length of 5microns was no more than 1.3 microns for all samples. More specifically,the Rmax was 0.6 microns for Test Sample 3-2, for example. The chlorinecontent was measured using XPS (X-ray Photoelectron Spectroscopy), butcomposition can also be studied using micro-EDX (Energy Dispersive X-raySpectroscopy) combined with a transmission electron microscope or usingSIMS (Secondary Ion Mass Spectrometry). TABLE 6 Pres- Temper- CoatingReaction gas composition sure ature layer (vol %) (kPa) (deg C.) AlN *¹AlCl₃: 1.0-5.0%, NH₃: 0.1-5.0%, 4.0-80 750-980 N₂: 20-50%, HCl:0.01-1.0%, H₂: rest AlCN *¹ AlCl₃: 1.0-5.0%, NH₃: 0.1-5.0%, 4.0-80750-980 N₂: 20-50%, CH₄: 0.5-5.0%, HCl: 0.01-1.0%, H₂: rest AlON *¹AlCl₃: 1.0-5.0%, NH₃: 0.1-5.0%, 4.0-80 750-980 N₂: 20-50%, CO₂:0.2-3.0%, HCl: 0.01-1.0%, H₂: rest AlN *² AlCl₃: 1.5%, NH₃: 1.0%, 5.01000 N₂: 40%, H₂: rest AlN *³ AlCl₃: 1.5%, NH₃: 3.0%, 13.3 950 N₂: 40%,HCl: 5.0%, H₂: rest AlON *² AlCl₃: 1.5%, NH₃: 6.0%, 6.8 1100 N₂: 40%,CO₂: 1.0%, H₂: rest TIN TiCl₄: 2.0%, N₂: 25%, H₂: rest 13.3 950 TiCTiCl₄: 2.0%, CN₄: 5%, H₂: rest 13.3 1050 granular TiCl₄: 4.0%, CH₄:4.0%, 14 1020 TiCN N₂: 20%, H₂: rest columnar TiCl₄: 3.0%, CH₃CN: 0.6%,4.0-80 800-950 TiCN N₂: 20%, H₂: rest ZrCN ZrCl₄: 1.0%, CH₃CN: 0.6%, 6.7890 N₂: 35%, H₂: rest TiZrCN TiCl₄: 1.5%, ZrCl₄: 1.0%, 6.7 975 CH₃CN:1.0%, N₂: 45%, H₂: rest TiCNO TiCl₄: 2.0%, CO₂: 2.5%, 6.7 975 N₂: 8%,H₂: rest TiBN TiCl₄: 2.0%, BCl₃: 5.0%, 13.3 950 N₂: 5.0%, H₂: rest HfCNHfCl₄: 1.0%, CH₃CN: 1.2%, 6.7 1025 N₂: 40%, H₂: rest α Al₂O₃ AlCl₃:2.0%, H₂S: 0.3%, 6.7 1050 CO₂: 5.0%, H₂: rest κ Al₂O₃ AlCl₃: 2.0%, CO₂:5.0%, 6.7 1000 CO: 0.5%, H₂: rest ZrO₂ ZrCl₄: 2.0%, CO₂: 7.0%, 6.7 1050H₂: rest Al₂O₃—ZrO₂ AlCl₃: 1.5%, ZrCl₄: 0.3%, 13.3 1070 CO₂: 9.0%, H₂:rest*¹ Chlorine content is more than 0 and no more than 0.5 atomic percent*² No chlorine*³ Chlorine content is more than 0.5 atomic percent

TABLE 7 Test sample Outermost Chlorine content No. layer (atomicpercent) 3-1 AlN *¹ 0.02 3-2 AlN *¹ 0.15 3-3 AlN *¹ 0.49 3-4 AlN *² 03-5 AlN *³ 0.90

Using the surface-coated throw-away inserts with the outermost layers asshown in Table 7, continuous cutting operations were performed using thecutting conditions shown in Table 8. The cutting time involved inreaching the tool life was measured. In a peeling resistance test,cutting operations were repeated, with the end of tool life defined tobe when flank face wear due to film peeling was at least 0.3 mm. In awear resistance test, tool life was defined to be when the flank facewear was at least 0.3 mm. The results of the tests are shown in Table 9.TABLE 8 Peeling resistance test Wear resistance test Workpiece S15C rodS45C rod 3 sec repetition test Speed V = 300 m/min V = 260 m/min Feed f= 0.3 mm/rev. f = 0.2 mm/rev. Cutting depth d = 1.0 mm d = 1.5 mmCutting oil None None

TABLE 9 Test Sample Cutting time (min) No. Peeling resistance test Wearresistance test 3-1 42 24 3-2 60 31 3-3 51 21 3-4 12 6 3-5 10 5

Based on the results, in the Test Samples 3-1 through 3-3, which havealuminum nitride layers with more than 0 and not more than 0.5 atomicpercent of chlorine on the outermost layer as shown in Table 9, superiorlubricity and improved welding resistance was observed even in drycutting. This improved welding resistance and provided superior peelingresistance by reducing cutting force. Also, since a predetermined TiCNfilm is used in the inner layer, the Test Samples 3-1-3-3 also providesuperior wear resistance. Furthermore, chipping did not take place withthese Test Samples 3-1-3-3. Thus superior chipping resistance andfracturing resistance are provided. Based on these factors, it can beseen that the Test Samples 3-1-3-3 provide longer cutting times andextended tool life.

TEST EXAMPLE 1-5

A cemented carbide substrate similar to the one used in the Test Example1-4 was prepared. Thermal CVD was performed on the surface of theobtained substrate to form a coating layer with the film formingconditions (gas composition, pressure, temperature) shown in Table 6. Inthis test, the following layers were formed, starting from the substrateside: TiN(0.5), columnar structure TiCN(4) or granular structureTiCN(4), TiBN(0.5), Al₂O₃—ZrO₂(2) and an outermost layer formed fromAlN*¹(3) (Test Sample 3-3 from Table 7). The numbers in parenthesesindicate film thickness in microns. Film thickness was controlled bycontrolling the film forming time. In this test, the aspect ratio andthe face with the maximum index of orientation of the columnar structureTiCN film are varied, as shown in Table 6, by varying the film formingpressure and temperature as well as by varying the surface roughness andgas conditions for the TiN film formed below the TiCN film. Morespecifically, the aspect ratio of the TiCN film was set to at least 3 byusing CH₃CN as the reaction gas, with the gas temperature set to 920 degC. and the pressure set to 6 kPa and the CH₃CN reaction gas beingintroduced gradually. Also, if the TiCN film maximum index oforientation is to be TC(422), for example, the surface roughness Rmax (5microns reference length) of the substrate is set to 0.09 microns andthe TiCN film is formed while adjusting the aspect ratio outward fromthe substrate (away from the substrate). Furthermore, for all the testsamples, the surface of the outermost layer was polished after formingthe outermost layer so that the section of the outermost layer aroundthe ridge line of the cutting edge that comes into contact with theworkpiece had a surface roughness Rmax of 0.4 microns for 5 micronsreference length when measured by observing tool cross-sections. Table10 shows TiCN film structure, aspect ratio, and the face with themaximum index of orientation TC. TABLE 10 Test Inner layer TiCN filmsample Aspect Face with Cutting time (min) No. Structure ratio maximumTC Wear resistance test 4-1 Columnar 5.2 311 21 4-2 Columnar 6.6 422 254-3 Columnar 3.1 220 19 4-4 Columnar 2.3 220 4 4-5 Columnar 3.5 420 54-6 Granular — 311 1

Using the surface-coated throw-away inserts with TiCN film inner layersas shown in Table 10, continuous cutting operations were performed usingthe cutting conditions described below. The cutting time involved inreaching the tool life was measured. The end of tool life was defined tobe when flank face wear was at least 0.3 mm. Table 10 shows the resultsfrom the test as well.

Workpiece: wear resistance test with SUS rod

Speed: V=200 m/min

Feed: f=0.2 mm/rev.

Depth of cut: d=1.5 mm

Cutting oil: none

The results show that with a TiCN film as an inner layer as in Table 10,a columnar structure provides superior wear resistance. Morespecifically, with Test Samples 4-1-4-3, which are formed with columnarstructure TiCN film at the inner layer with an aspect ratio of at least3 and a maximum index of orientation of TC(311), TC(220), or TC(422),wear resistance is especially superior and tool life is longer, evenwhen dry cutting. The longer tool life is believed to be because of thesuperior lubricity of the outermost layer and the use of a predeterminedTiCN film with superior wear resistance as the inner layer.

TEST EXAMPLE 1-6

A cemented carbide substrate similar to the one used in the Test Example1-4 was prepared. Thermal CVD was performed on the surface of theobtained substrate to form a coating layer with the film formingconditions (gas composition, pressure, temperature) shown in Table 6. Inthis test, the film forming conditions were controlled so that columnarstructure TiCN films had an aspect ratio of at least 3 and the maximumindex of orientation was TC(311), TC(220), or TC(422). Table 11 showsthe composition, film thicknesses, and the film thickness of the entirecoating layer (total film thickness). In Table 11, the films areindicated sequentially as the first film, the second film, and the likestarting from the film closest to the substrate. TABLE 11 Test TotalSam- First film Second film Third film Fourth film Fifth film Sixth filmThick- Cutting ple Thick- Thick- Thick- Thick- Thick- Thick- ness timeNo. Type ness Type ness Type ness Type ness Type ness Type ness μm min5-1  colum- 5.0 AlN*¹ 2.0 7.0 21 nar TiCN 5-2  colum- 0.5 ZrCN 7.0 AlN*¹0.5 8.0 31 nar TiCN 5-3  TiN 1.0 colum- 4.5 TiC 1.5 TiCNO 1.0 κ Al₂O₃3.0 AlCN*¹ 5.0 16.0 37 nar TiCN 5-4  TiN 0.3 colum- 6.5 TiBN 0.5 κ Al₂O₃1.5 TiN 0.3 AlN*¹ 3.0 12.1 27 nar TiCN 5-5  TiN 0.5 colum- 20.0 Al₂O₃—5.0 AlN*¹ 2.0 27.5 35 nar ZrO₂ TiCN 5-6  colum- 3.0 TiZrCN 5.0 ZrO₂ 2.3Al₂O₃— 2.5 AlON*¹ 1.7 14.5 26 nar ZrO₂ TiCN 5-7  colum- 3.2 TiN 0.5 HfCN4.3 AlCN*¹ 2.5 10.5 23 nar TiCN 5-8  colum- 0.5 TiBN 1.3 α Al₂O₃ 5.0AlN*¹ 0.05 6.85 26 nar TiCN 5-9  HfCN 3.5 α Al₂O₃ 1.5 TiCNO 2.3 colum-6.5 TiN 0.7 AlCN*¹ 0.7 15.2 32 nar TiCN 5-10 colum- 5.0 TiZrCN 14.0AlCN*¹ 9.0 28 32 nar TiCN 5-11 TiN 0.5 colum- 4.5 AlCN*¹ 0.5 AlN*¹ 0.56.0 25 nar TiCN 5-12 TiN 0.5 TiCNO 2.0 colum- 6.0 TiBN 0.5 κ Al₂O₃ 1.5AlCN*¹ 0.7 11.2 23 nar TiCN 5-13 colum- 2.0 HfCN 2.0 TiN 1.0 5.0 6 narTiCN 5-14 TiN 0.5 colum- 5.0 TiCNO 0.5 ZrO₂ 2.0 colum- 0.1 TiN 2.0 10.17 nar nar TiCN TiCN 5-15 colum- 0.5 AlON*¹ 2.0 α Al₂O₃ 3.0 TiN 1.5 7.0 5nar TiCN 5-16 colum- 0.07 AlN*¹ 0.02 0.09 8 nar TiCN 5-17 colum- 0.5ZrCN 4.0 AlN*¹ 0.02 4.52 11 nar TiCN 5-18 TiN 0.5 colum- 3.0 TiCNO 11.0α Al₂O₃ 3.5 Al₂O₃— 7.0 AlCN*¹ 10.0 35.0 8 nar ZrO₂ TiCN 5-19 colum- 4.0TiBN 2.0 ZrO₂ 2.0 AlCN*¹ 8.0 16.0 14 nar TiCN 5-20 TiN 0.2 colum- 0.8ZrCN 4.0 AlON*² 1.3 6.3 7 nar TiCN 5-21 colum- 10.0 AlCN*¹ 4.0 14.0 10nar TiCN

Using the surface-coated throw-away inserts with coating layers as shownin Table 11, continuous cutting operations were performed using thecutting conditions described below. The cutting time involved inreaching the tool life was measured. The end of tool life was defined tobe when flank face wear was at least 0.3 mm. Table 11 shows the resultsfrom the test as well.

Workpiece: 15-second repetitive wear resistance test with SCM435 rod

Speed: V=180 m/min

Feed: f=0.2 mm/rev.

Depth of cut: d=1.5 mm

Cutting oil: none

As a result, it was found as shown in Table 11 that, compared to theother test samples, Test Samples 5-1-5-12, 5-16-5-19, 5-21, which had analuminum nitride film containing a predetermined amount of chlorine asthe outermost layer and a columnar structure TiCN film inner layer withan aspect ratio of at least 3 and a maximum index of orientation ofTC(311), TC(220), or TC(422), provided superior lubricity and superiorwear resistance.

Also, the results shown in Table 11 indicate that it is preferable forthe outermost layer to be at least 0.03 microns and for the total filmthickness to be at least 0.1 microns and no more than 30 microns.Furthermore, it can be seen that it is preferable for the outermostlayer to have no more than ½ the total thickness of the inner layer.

The inserts from the test sample 5-1-5-21 were all cut and the surfaceroughness relative to a 5 micron reference length was measured for thearea of the outermost layer near the ridge line of the cutting edge thatcomes into contact with the workpiece. As a result, it was found thatRmax was no more than 1.3 microns for all inserts except Test Sample5-21, while the Rmax of the Test Sample 5-21 was 1.7 microns. For TestSample 5-21, a #1500 diamond paste was used to polish the area of theoutermost layer near the ridge line of the cutting edge that comes intocontact with the workpiece. When the method described above was used tomeasure surface roughness after polishing, Rmax was 0.52 microns. When acutting test was performed under the same cutting conditions using thepolished insert, the tool life was 24 min. This is believed to be causedby a reduction in the cutting force resulting from less roughness at thearea of the outermost layer near the ridge line of the cutting edge thatcomes into contact with the workpiece. When the surface roughness ofTest Sample 5-3 was measured as described above, the Rmax was 0.76microns, but when the cutting edge was polished in the same manner, thetool life after another cutting operation was found to be significantlyimproved, at 48 min.

TEST EXAMPLE 1-6′

Surface-coated inserts similar to those of Test Samples 5-1-5-21 wereprepared and cutting tests were performed under the cutting conditionsdescribed below. Crater wear (area: mm²) was then measured for apredetermined cutting length (500 m).

Workpiece: S50C

Speed: V=250 m/min

Feed: f=0.3 mm/rev.

Depth of cut: d=1.5 mm

Cutting oil: none

The results showed that Test Samples 5-1-5-12, 5-16-5-19, and 5-21 hadless crater wear compared to the other samples. For example, the resultsfor Test Samples 5-4, 5-5, and 5-6 were 0.3 mm², 0.27 mm², and 0.29 mm²,respectively.

TEST EXAMPLE 1-7

Using the substrate described below, a coating film having a compositionsimilar to that of Test Sample 5-2 from Table 11 was formed using awidely known PVD method. Surface-coated inserts were formed by addingchlorine to the outermost layer using ion implantation after the coatinglayer was formed. Cutting tests were performed under cutting conditionssimilar to those of Test Example 1-6.

The chlorine content of the outermost layer was 0.18 atomic percent inall cases.

1. JIS standard: P20 cermet cutting insert (T1200A, Sumitomo ElectricHardmetal Corp. Ltd.)

2. Ceramic cutting insert (W80, Sumitomo Electric Hardmetal Corp. Ltd.)

3. Silicon nitride cutting insert (NS260, Sumitomo Electric HardmetalCorp. Ltd.)

4. Cubic boron nitride cutting insert (BN250, Sumitomo ElectricHardmetal Corp. Ltd.)

The results indicated that all the coated inserts provided superiorlubricity and wear resistance.

Based on this, it can be seen that tool life can be improved in the samemanner as when a cemented carbide is used as described above.

SECOND EXAMPLE

The present invention will be described in more detail, using end millsas an example.

TEST EXAMPLE 2-1

Two-edge square end mill substrates (solid end mills) formed fromcemented carbide corresponding to JIS Z20 (10 mm diameter) wereprepared. Thermal CVD, which is a chemical vapor deposition technique,was performed to form a coating layer on the substrate at the surface ofthe areas (body) associated with cutting. In this test, the followinglayers were formed, starting from the substrate side: an inner layerformed from TiN(0.5), TiCN(4), TiBN(0.5), κ-Al₂O₃(1) and an outermostlayer formed from AlN (1.5). The numbers in parentheses indicate filmthickness in microns. Table 12 shows an example of film formingconditions for each film. Specifically, the composition of the reactiongas (percent by volume), the pressure applied when forming the film(kPa), and the film forming temperature (deg C) are shown. Filmthickness was controlled by controlling the film forming time. Testsamples in which the AlN film at the outermost layer have differentchlorine contents were prepared by varying the film forming conditionsas shown in Table 12. Table 13 shows chlorine content at the outermostlayer. Specifically, samples with more than 0 and no more than 0.5atomic percent of chlorine, samples with more than 0.5 atomic percent ofchlorine, and samples with no chlorine in the outermost layer wereprepared. Chlorine content was varied as shown in Table 12 by varyingthe proportion of hydrogen chloride (HCl) in the reaction gas. Also,depending on the amount of hydrogen chloride, the film forming pressureand the film forming temperature were varied as appropriate.Furthermore, the surface roughness at sites on the outermost layer nearthe ridge line of the cutting edge at areas that come into contact withthe workpiece were studied for test samples containing more than 0 andno more than 0.5 atomic percent of chlorine in the outermost layer.Observation of the tool cross-sections showed that the Rmax for areference length of 5 microns was no more than 1.3 microns for allsamples. More specifically, the Rmax was 0.6 microns for Test Sample6-2, for example. The chlorine content was measured using XPS (X-rayPhotoelectron Spectroscopy), but composition can also be studied usingmicro-EDX (Energy Dispersive X-ray Spectroscopy) combined with atransmission electron microscope or using SIMS (Secondary Ion MassSpectrometry). Also, the Knoop hardness for each of the layers in thetest samples was studied, and it was found that in all cases theoutermost AlN film was softer than the inner TiCN film layer. TABLE 12Pres- Temper- Coating Reaction gas composition sure ature layer (vol %)(kPa) (deg C.) AlN *¹ AlCl₃: 1.0-5.0%, NH₃: 0.1-5.0%, 4.0-80 750-980 N₂:20-50%, HCl: 0.01-1.0%, H₂: rest AlCN *¹ AlCl₃: 1.0-5.0%, NH₃: 0.1-5.0%,4.0-80 750-980 N₂: 20-50%, CH₄: 0.5-5.0%, HCl: 0.01-1.0%, H₂: rest AlON*¹ AlCl₃: 1.0-5.0%, NH₃: 0.1-5.0%, 4.0-80 750-980 N₂: 20-50%, CO₂:0.2-3.0%, HCl: 0.01-1.0%, H₂: rest AlN *² AlCl₃: 1.5%, NH₃: 1.0%, 5.01000 N₂: 40%, H₂: rest AlN *³ AlCl₃: 1.5%, NH₃: 3.0%, 13.3 950 N₂: 40%,HCl: 5.0%, H₂: rest AlON *² AlCl₃: 1.5%, NH₃: 6.0%, 6.8 1100 N₂: 40%,CO₂: 1.0%, H₂: rest TiN TiCl₄: 2.0%, N₂: 25%, H₂: rest 13.3 950 TiCTiCl₄: 2.0%, CN₄: 5%, H₂: rest 13.3 1050 TiCN TiCl₄: 2.0%, CH₃CN: 0.6%,6.7-80 800-950 N₂: 20%, H₂: rest ZrCN ZrCl₄: 1.0%, CH₃CN: 0.6%, 6.7 890N₂: 35%, H₂: rest TiZrCN TiCl₄: 1.5%, ZrCl₄: 1.0%, 6.7 975 CH₃CN: 1.0%,N₂: 45%, H₂: rest TiCNO TiCl₄: 2.0%, CO₂: 2.5%, 6.7 975 N₂: 8%, H₂: restTiBN TiCl₄: 2.0%, BCl₃: 5.0%, 13.3 950 N₂: 5.0%, H₂: rest HfCN HfCl₄:1.0%, CH₃CN: 1.2%, 6.7 1025 N₂: 40%, H₂: rest α Al₂O₃ AlCl₃: 2.0%, H₂S:0.3%, 6.7 1050 CO₂: 5.0%, H₂: rest κ Al₂O₃ AlCl₃: 2.0%, CO₂: 5.0%, 6.71000 CO: 0.5%, H₂: rest ZrO₂ ZrCl₄: 2.0%, CO₂: 7.0%, 6.7 1050 H₂: restAl₂O₃—ZrO₂ AlCl₃: 1.5%, ZrCl₄: 0.3%, 13.3 1070 CO₂: 9.0%, H₂: rest*¹ Chlorine content is more than 0 and no more than 0.5 atomic percent*² No chlorine*³ Chlorine content is more than 0.5 atomic percent

TABLE 13 Test sample Outermost Chlorine content No. layer (atomic %) 6-1AlN *¹ 0.03 6-2 AlN *¹ 0.18 6-3 AlN *¹ 0.48 6-4 AlN *² 0 6-5 AlN *³ 0.98

Using the cutting conditions shown in Table 14, the cutting efficiencyof surface-coated end mills with outermost layers as shown in Table 13was observed. For the cutting conditions 1, the wear for a fixed cuttinglength (150 m) was measured. In this test, the flank face wear (microns)on the peripheral cutting edge was measured. For the cutting conditions2, a fixed boring operation (10 mm diameter) was performed. The torqueapplied during boring was measured and the state after changing to afixed slot milling operation (50 mm) after the boring operation wasobserved. The results of the tests are shown in Table 15. TABLE 14Cutting conditions 1 Cutting conditions 2 Side milling 10 mm boring,then 50 mm fluting Workpiece: S50C Workpiece: SKD11 Speed: V = 300 m/minSpeed: V = 80 m/min Feed per cutting edge: ft = 0.1 mm Feed: Boring 0.07mm/rev., Axial cutting depth: Ad = 8 mm Fluting 0.15 mm/t Radial cuttingdepth: Rd = 0.5 mm (per cutting edge) Cutting oil: None Cutting oil:None Cutting distance: 150 m

TABLE 15 Test Cutting conditions 1 Cutting conditions 2 sample Flankface wear Maximum torque No. (peripheral cutting edge, microns) (N · cm)6-1 55 610 6-2 31 410 6-3 42 550 6-4 92 1050 (breakage during fluting)6-5 115 1120 (chipping) (breakage during fluting)

Based on the results, in Test Samples 6-1 through 6-3, which havealuminum nitride layers with more than 0 and not more than 0.5 atomicpercent of chlorine on the outermost layer as shown in Table 15 and aninner layer with films having a predetermined composition, wear wasreduced and superior lubricity and improved fracturing resistance due toreduced cutting force was observed even in dry cutting. Because TestSamples 6-1-6-3 were formed with a coating layer having superiorlubricity, chip ejection qualities were good. As a result, torqueincreases were limited and breaking resistance was improved, allowingproblem-free cutting. With Test Samples 6-4, 6-5, torque increased andbreakage occurred when switching to slot milling. Furthermore, theseTest Samples 6-1-6-3 provided superior welding resistance and peeling ofthe coating layer and the like did not take place. Based on thesefactors, it could be seen that Test Samples 6-1-6-3 were able to extendtool life.

TEST EXAMPLE 2-2

Substrates similar to those from the cemented carbide end millsubstrates used in the Test Example 2-1 were prepared. Thermal CVD wasperformed on the area associated with cutting, and coating layers wereformed under the film forming conditions (gas composition, pressure,temperature) shown in Table 12. Table 16 shows the composition, filmthicknesses, and the film thickness of the entire coating layer (totalfilm thickness). In Table 16, the films are indicated sequentially asthe first film, the second film, and the like starting from the filmclosest to the substrate. TABLE 16 Test Total Flank Sam- First filmSecond film Third film Fourth film Fifth film Sixth film thick- face pleThick- Thick- Thick- Thick- Thick- Thick- ness wear No. Type ness Typeness Type ness Type ness Type ness Type ness μm μm 7-1  TiCN 3.0 AlN*¹1.0 4.0 62 7-2  TiN 0.5 ZrCN 7.0 AlN*¹ 0.5 8.0 35 7-3  TiN 1.0 TiCN 4.5TiC 1.5 TiCNO 1.0 κ Al₂O₃ 3.0 AlCN*¹ 5.0 16.0 33 7-4  TiN 0.3 TiCN 6.5TiBN 0.5 κ Al₂O₃ 1.5 TiN 0.3 AlN*¹ 3.0 12.1 53 7-5  TiN 0.5 TiCN 14.0Al₂O₃— 5.0 AlN*¹ 2.0 21.5 31 ZrO₂ 7-6  TiCN 3.0 TiZrCN 5.0 ZrO₂ 2.3Al₂O₃— 2.5 AlON*¹ 1.7 14.5 44 ZrO₂ 7-7  TiCN 3.2 TiN 0.5 HfCN 4.3 AlCN*¹2.5 10.5 60 7-8  TiN 0.5 TiBN 1.3 α Al₂O₃ 5.0 AlN*¹ 0.05 6.85 52 7-9 HfCN 3.5 α Al₂O₃ 1.5 TiCNO 2.3 TiCN 6.5 TiN 0.7 AlCN*¹ 0.7 15.2 41 7-10TiN 2.0 TiZrCN 14.0 AlCN*¹ 7.0 2.3 35 7-11 TiN 0.5 TiCN 4.5 AlCN*¹ 0.5AlN*¹ 0.5 6.0 56 7-12 TiN 0.5 TiCNO 2.0 TiCN 6.0 TiBN 0.5 κ Al₂O₃ 1.5AlCN*¹ 0.7 11.2 54 7-13 HfCN 4.0 TiN 1.0 5.0 135 7-14 TiN 0.5 TiCN 5.0TiCNO 0.5 ZrO₂ 2.0 TiCN 0.1 TiN 2.0 10.1 180 7-15 TiN 0.5 AlON*¹ 2.0 αAl₂O₃ 3.0 TiN 1.5 7.0 128 7-16 ZrCN 0.07 AlN*¹ 0.02 0.09 82 7-17 TiN 0.5ZrCN 4.0 AlN*¹ 0.02 4.52 95 7-18 TiN 0.5 TiCN 3.0 TiCNO 9.0 α Al₂O₃ 3.5Al₂O₃— 5.0 AlCN*¹ 8.0 29.0 98 ZrO₂ 7-19 TiCN 4.0 TiBN 2.0 ZrO₂ 2.0AlCN*¹ 7.0 15.0 92 7-20 TiN 1.0 ZrCN 4.0 AlON*² 1.3 6.3 210 7-21 AlN*¹5.0 5.0 165 7-22 TiN 3.0 AlCN*¹ 1.0 4.0 88 7-23 TiZrCN 10.0 AlCN*¹ 4.014.0 93

The surface-coated end mills with the coatings shown in Table 16 wereused to perform side milling under the conditions described below, andwear for a fixed cutting length (100 m) was measured. In this test, theflank face wear (microns) on the peripheral cutting edge was measured.Table 16 shows the results from the test as well.

End mill side milling

Workpiece: SUS304

Speed: V=130 m/min

Feed per cutting edge: ft=0.03 mm

Axial cutting depth: Ad=8 mm

Radial cutting depth: Rd=0.16 mm

Cutting oil: none

Cutting length: 100 m

As a result, it was found as shown in Table 16 that, compared to theother test samples, Test Samples 7-1-7-12, 7-16-7-19, 7-22, 7-23, whichhad an aluminum nitride film containing a predetermined amount ofchlorine as the outermost layer and an inner layer with films having apredetermined composition, provided superior lubricity and superior wearresistance.

Also, the results shown in Table 16 indicate that it is preferable forthe outermost layer to be at least 0.03 microns and for the total filmthickness to be at least 0.1 microns and no more than 24 microns.Furthermore, it can be seen that it is preferable for the outermostlayer to have no more than ½ the total thickness of the inner layer.

The end mills from test sample 7-1-7-23 were all cut and the surfaceroughness relative to a 5 micron reference length was measured for thearea of the outermost layer near the ridge line of the cutting edge ofthe peripheral cutting edge that comes into contact with the workpiece.As a result, it was found that Rmax was no more than 1.3 microns for allend mills except Test Sample 7-22, while the Rmax of Test Sample 7-22was 1.7 microns. For Test Sample 7-22, a #1500 diamond paste was used topolish the area of the outermost layer of the peripheral cutting edgenear the ridge line of the cutting edge that comes into contact with theworkpiece. When the method described above was used to measure surfaceroughness after polishing, Rmax was 0.52 microns. When side milling wasperformed under the same cutting conditions using the polished end mill,the flank face wear was 65 microns. This is believed to be caused by areduction in the cutting force resulting from less roughness at the areaof the outermost layer near the ridge line of the cutting edge thatcomes into contact with the workpiece. When the surface roughness ofTest Sample 7-1 was measured as described above, the Rmax was 0.9microns, but when the cutting edge was polished in the same manner, theflank face wear after another cutting operation was found to besignificantly improved, at 35 microns.

Furthermore, a coating film was formed on Test Sample 7-23 to make thefilm hardness of the inner layer lower than that of the outermost layer.Then, the hardnesses of the films forming the coating layers of TestSamples 7-1-7-20, 7-22, and 7-23 were measured. The film hardness of theoutermost layer was lower than that of at least one film of the innerlayer for all the end mills, with the exception of Test Sample 7-23.With Test Sample 7-23, the film hardness of the outermost layer washigher than that of the inner layer. As a result, it is believed thatthe cutting efficiency of Test Sample 7-23 was reduced.

TEST EXAMPLE 2-2′

Surface-coated end mills similar to those of Test Samples 7-1-7-23 wereprepared and cutting tests were performed under the cutting conditionsdescribed below. Crater wear (width) was then measured for apredetermined cutting length (50 m). Measurements were made of craterwear widths on the peripheral cutting edge. Because end mills have athree-dimensional shape, this width was measured obliquely. Morespecifically, crater wear width was measured by observing from a fixedangle.

Results were evaluated based on these measurements by comparing thedifferent test samples.

Workpiece: S50C

Speed: V=100 m/min

Feed: f=0.05 mm/t

Cutting depth: Ad=10 mm Rd=0.6 mm

Cutting oil: none (air blower)

The results indicated that crater wear was lower for Test Samples7-1-7-12, 7-16-7-19, 7-22, 7-23 compared to the other test samples. Forexample, if the wear width of Test Sample 7-14 is defined as 1, TestSamples 7-3, 7-6 had the values 0.44 and 0.52 respectively.

TEST EXAMPLE 2-3

Surface-coated end mills were prepared using the substrate describedbelow with a widely known PVD method being used to form a coating layerhaving a composition similar to that of Test Samples 7-2, 7-13 fromTable 16. For the end mill with a coating layer having a compositionsimilar to that of the Test Sample 7-2, the surface-coated end mill wasformed by adding chlorine to the outermost layer using ion implantationafter the coating layer was formed. Then, side milling was performedusing the same cutting conditions as Test Example 2-2. The coatinglayers were all formed at areas associated with cutting.

The test samples with the coating layer from Test Sample 7-2 all had achlorine content of 0.2 atomic percent on the outermost layer.

1 Brazed end mill substrate formed from cemented carbide correspondingto JIS Z20 (cutting section is cemented carbide)

2 Two-edge square end mill substrate formed from JIS-standard P20 cermet(10 mm diameter)

3 Brazed ball mill substrate formed from cubic boron nitride (SumitomoElectric Hardmetal Corp. Ltd., BN300) (cutting section is cubic boronnitride)

The results indicated that all the surface-coated end mills formed withthe coating layer from Test Sample 7-2 provided superior lubricity andwear resistance. It was found that the tool life was at least twice thatof end mills formed with the conventional coating layer from Test Sample7-13.

TEST EXAMPLE 2-4

Two-edge square end mill substrates (solid end mills) formed fromcemented carbide corresponding to JIS Z20 (10 mm diameter) wereprepared. Thermal CVD, which is a chemical vapor deposition technique,was performed to form a coating layer on the substrate at the surface ofthe areas (body) associated with cutting. In this test, the followinglayers were formed, starting from the substrate side: TiN(0.5), columnarstructure TiCN(4), TiBN(0.5), κ-Al₂O₃(1), and an outermost layer formedfrom AlN (1.5). The numbers in parentheses indicate film thickness inmicrons. Table 17 shows an example of film forming conditions for eachfilm. Specifically, the composition of the reaction gas (percent byvolume), the pressure applied when forming the film (kPa), and the filmforming temperature (deg C) are shown. Film thickness was controlled bycontrolling the film forming time. In this test, the TiCN film has acolumnar structure with an aspect ratio of 4.1 and the index oforientation TC is highest at the (311) face. More specifically, the TiNfilm formation conditions (gas composition, pressure, temperature) wereset up so that the reaction gas was CH₃CN, the temperature was 900 degC., the pressure was 8 kPa, and the surface roughness Rmax (5 micronsreference length) of the TiN film formed below the TiCN film was 0.1microns. Test samples in which the AlN film at the outermost layer havedifferent chlorine contents were prepared by varying the film formingconditions as shown in Table 17. Table 18 shows chlorine content at theoutermost layer. Specifically, samples with more than 0 and no more than0.5 atomic percent of chlorine, samples with more than 0.5 atomicpercent of chlorine, and samples with no chlorine were prepared.Chlorine content was varied as shown in Table 17 by varying theproportion of hydrogen chloride (HCl) in the reaction gas. Also,depending on the amount of hydrogen chloride, the film forming pressureand the film forming temperature were varied as appropriate.Furthermore, the surface roughness at sites on the outermost layer nearthe ridge line of the cutting edge at areas that come into contact withthe workpiece were studied for test samples containing more than 0 andno more than 0.5 atomic percent of chlorine in the outermost layer.Observation of the tool cross-sections showed that the Rmax for areference length of 5 microns was no more than 1.3 microns for allsamples. More specifically, the Rmax was 0.6 microns for Test Sample8-2, for example. The chlorine content was measured using XPS (X-rayPhotoelectron Spectroscopy), but composition can also be studied usingmicro-EDX (Energy Dispersive X-ray Spectroscopy) combined with atransmission electron microscope or using SIMS (Secondary Ion MassSpectrometry). TABLE 17 Pres- Temper- Coating Reaction gas compositionsure ature layer (vol %) (kPa) (deg C.) AlN *¹ AlCl₃: 1.0-5.0%, NH₃:0.1-5.0%, 4.0-80 750-980 N₂: 20-50%, HCl: 0.01-1.0%, H₂: rest AlCN *¹AlCl₃: 1.0-5.0%, NH₃: 0.1-5.0%, 4.0-80 750-980 N₂: 20-50%, CH₄:0.5-5.0%, HCl: 0.01-1.0%, H₂: rest AlON *¹ AlCl₃: 1.0-5.0%, NH₃:0.1-5.0%, 4.0-80 750-980 N₂: 20-50%, CO₂: 0.2-3.0%, HCl: 0.01-1.0%, H₂:rest AlN *² AlCl₃: 1.5%, NH₃: 1.0%, 5.0 1000 N₂: 40%, H₂: rest AlN *³AlCl₃: 1.5%, NH₃: 3.0%, 13.3 950 N₂: 40%, HCl: 5.0%, H₂: rest AlON *²AlCl₃: 1.5%, NH₃: 6.0%, 6.8 1100 N₂: 40%, CO₂: 1.0%, H₂: rest TiN TiCl₄:2.0%, N₂: 25%, H₂: rest 13.3 950 TiC TiCl₄: 2.0%, CN₄: 5%, H₂: rest 13.31050 Granular TiCl₄: 4.0%, CH₄: 4.0%, 14 1020 TiCN N₂: 20%, H₂: restColumnar TiCl₄: 3.0%, CH₃CN: 0.6%, 4.0-80 800-950 TiCN N₂: 20%, H₂: restZrCN ZrCl₄: 1.0%, CH₃CN: 0.6%, 6.7 890 N₂: 35%, H₂: rest TiZrCN TiCl₄:1.5%, ZrCl₄: 1.0%, 6.7 975 CH₃CN: 1.0%, N₂: 45%, H₂: rest TiCNO TiCl₄:2.0%, CO₂: 2.5%, N₂: 8%, 6.7 975 H₂: rest TiBN TiCl₄: 2.0%, BCl₃: 5.0%,13.3 950 N₂: 5.0%, H₂: rest HfCN HfCl₄: 1.0%, CH₃CN: 1.2%, 6.7 1025 N₂:40%, H₂: rest α Al₂O₃ AlCl₃: 2.0%, H₂S: 0.3%, 6.7 1050 CO₂: 5.0%, H₂:rest κ Al₂O₃ AlCl₃: 2.0%, CO₂: 5.0%, 6.7 1000 CO: 0.5%, H₂: rest ZrO₂ZrCl₄: 2.0%, CO₂: 7.0%, 6.7 1050 H₂: rest Al₂O₃— ZrO₂ AlCl₃: 1.5%,ZrCl₄: 0.3%, 13.3 1070 CO₂: 9.0%, H₂: rest*¹ Chlorine content is more than 0 and no more than 0.5 atomic percent*² No chlorine*³ Chlorine content is more than 0.5 atomic percent

TABLE 18 Test sample Outermost Chlorine content No. layer (atomic %) 8-1AlN *¹ 0.03 8-2 AlN *¹ 0.18 8-3 AlN *¹ 0.48 8-4 AlN *² 0 8-5 AlN *³ 0.98

Using the cutting conditions shown in Table 19, the cutting efficiencyof surface-coated end mills with outermost layers as shown in Table 18was observed. For the cutting conditions I, the wear for a fixed cuttinglength (150 m) was measured. In this test, the flank face wear (microns)on the peripheral cutting edge was measured. For the cutting conditionsII, a fixed boring operation (10 mm diameter) was performed. The torqueapplied during boring was measured and the state after changing to afixed slot milling operation (50 mm) after the boring operation wasobserved. The results of the tests are shown in Table 20. TABLE 19Cutting conditions I Cutting conditions II Side milling 10 mm boring, 50mm fluting Workpiece: S50C Workpiece: SKD11 Speed: V = 300 m/min Speed:V = 80 m/min Feed per cutting Feed: Boring 0.07 mm/rev., edge: ft = 0.1mm Fluting 0.15 mm/t Axial cutting depth: (per cutting edge) Ad = 8 mmRadial cutting depth: Rd = 0.5 mm Cutting oil: none Cutting oil: noneCutting distance: 150 m

TABLE 20 Test Cutting conditions I Cutting conditions II Sample Flankface wear Maximum torque No. (peripheral cutting edge, microns) (N · cm)8-1 42 680 8-2 21 430 8-3 35 510 8-4 85 1110 (Breakage during fluting)8-5 121 1050 (Chipping) (Breakage during fluting)

Based on the results, the Test Samples 8-1 through 8-3, which havealuminum nitride layers with more than 0 and not more than 0.5 atomicpercent of chlorine on the outermost layer as shown in Table 20 andpredetermined inner TiCN film layers, wear was reduced and superiorlubricity and improved wear resistance and fracturing resistance due toreduced cutting force was observed even in dry cutting. Because TestSamples 8-1-8-3 were formed with a coating layer having superiorlubricity, chip ejection qualities were good. As a result, torqueincreases were limited and breaking resistance was improved, allowingproblem-free cutting. With Test Samples 8-4, 8-5, torque increased andbreakage occurred when switching to slot milling. Furthermore, theseTest Samples 8-1-8-3 provided superior welding resistance and peeling ofthe coating layer and the like did not take place. Based on thesefactors, it was shown that Test Samples 8-1-8-3 were able to extend toollife.

TEST EXAMPLE 2-5

Substrates similar to those from the cemented carbide end millsubstrates used in Test Example 2-4 were prepared. Thermal CVD wasperformed on the surfaces of locations associated with cutting, andcoating layers were formed under the film forming conditions (gascomposition, pressure, temperature) shown in Table 17. In this test, thefollowing layers were formed, starting from the substrate side:TiN(0.5), columnar structure TiCN(4) or granular structure TiCN(4),TiBN(0.5), Al₂O₃—ZrO₂(1), and an outermost layer formed from AlN*¹(1.5)(Test Sample 8-3 from Table 18). The numbers in parentheses indicatefilm thickness in microns. Film thickness was controlled by controllingthe film forming time. In this test, the aspect ratio and the face withthe maximum index of orientation of the columnar structure TiCN film arevaried, as shown in Table 17, by varying the film forming pressure andtemperature as well as by varying the surface roughness and gasconditions for the TiN film formed below the TiCN film. Morespecifically, the aspect ratio of the TiCN film was set to at least 3 byusing CH₃CN as the reaction gas, with the gas temperature set to 920 degC. and the pressure set to 6 kPa and the CH₃CN reaction gas beingintroduced gradually. Also, if the TiCN film maximum index oforientation is to be TC(422), for example, the surface roughness Rmax (5microns reference length) of the substrate is set to 0.09 microns andthe TiCN film is formed while adjusting the aspect ratio outward fromthe substrate (away from the substrate). Furthermore, for all the testsamples, the surface of the outermost layer was polished after formingthe outermost layer so that the section of the outermost layer aroundthe ridge line of the cutting edge that comes into contact with theworkpiece had a surface roughness Rmax of 0.4 microns for 5 micronsreference length when measured by observing tool cross-sections. Table21 shows TiCN film structure, aspect ratio, and the face with themaximum index of orientation TC. TABLE 21 Test Inner layer TiCN filmFlank wear Sample Aspect Face with (outer perimeter, No. Structure ratiomaximum TC microns) 9-1 Columnar 5.3 311 72 9-2 Columnar 6.8 422 64 9-3Columnar 3.3 220 85 9-4 Columnar 2.4 220 140 9-5 Columnar 3.8 420 1829-6 Granular — 311 255(Chipping)

The surface-coated end mills with TiCN film at the inner layer shown inTable 21 were used to perform side milling under the conditionsdescribed below, and flank face wear (microns) on the outer perimeterfor a fixed cutting length (80 m) was measured. Table 21 shows theresults from the test as well.

End mill side milling

Workpiece: SKD11

Speed: V=250 m/min

Feed per cutting edge: ft=0.05 mm

Axial cutting depth: Ad=8 mm

Radial cutting depth: Rd=0.15 mm

Cutting oil: none

Cutting length: 80 m

The results show that with a TiCN film at the inner layer as in Table21, a columnar structure provides superior wear resistance. Morespecifically, with the Test Samples 9-1-9-3, which are formed withcolumnar structure TiCN film at the inner layer with an aspect ratio ofat least 3 and a maximum index of orientation of TC(311), TC(220), orTC(422), wear resistance is especially superior, even when dry cutting.The reduced wear is believed to be because of the superior lubricity ofthe outermost layer and the use of a predetermined TiCN film withsuperior wear resistance as the inner layer.

TEST EXAMPLE 2-6

Substrates similar to those from the cemented carbide end millsubstrates used in Test Example 2-4 were prepared. Thermal CVD wasperformed on locations associated with cutting, and coating layers wereformed under the film forming conditions (gas composition, pressure,temperature) shown in Table 17. In this test, the film formingconditions were controlled so that columnar structure TiCN films had anaspect ratio of at least 3 and the maximum index of orientation wasTC(311), TC(220), or TC(422). Table 22 shows the composition, filmthicknesses, and the film thickness of the entire coating layer (totalfilm thickness). In Table 22, the films are indicated sequentially asthe first film, the second film, and the like starting from the filmclosest to the substrate. TABLE 22 Test Total Flank Sam- First filmSecond film Third film Fourth film Fifth film Sixth layer thick- faceple Thick- Thick- Thick- Thick- Thick- Thick- ness wear No. Type nessType ness Type ness Type ness Type ness Type ness μm μm 10-1  colum- 3.0AlN*¹ 1.0 4.0 52 nar TiCN 10-2  colum- 0.5 ZrCN 7.0 AlN*¹ 0.5 8.0 31 narTiCN 10-3  TiN 1.0 colum- 4.5 TiC 1.5 TiCNO 1.0 κ Al₂O₃ 3.0 AlCN*¹ 5.016.0 34 nar TiCN 10-4  TiN 0.3 colum- 6.5 TiBN 0.5 κ Al₂O₃ 1.5 TiN 0.3AlN*¹ 3.0 12.1 48 nar TiCN 10-5  TiN 0.5 colum- 14.0 Al₂O₃— 5.0 AlN*¹2.0 21.5 26 nar ZrO₂ TiCN 10-6  colum- 3.0 TiZrCN 5.0 ZrO₂ 2.3 Al₂O₃—2.5 AlON*¹ 1.7 14.5 44 nar ZrO₂ TiCN 10-7  colum- 3.2 TiN 0.5 HfCN 4.3AlCN*¹ 2.5 10.5 51 nar TiCN 10-8  colum- 0.5 TiBN 1.3 α Al₂O₃ 5.0 AlN*¹0.05 6.85 54 nar TiCN 10-9  HfCN 3.5 α Al₂O₃ 1.5 TiCNO 2.3 colum- 6.5TiN 0.7 AlCN*¹ 0.7 15.2 38 nar TiCN 10-10 colum- 5.0 TiZrCN 10.0 AlCN*¹7.0 22 40 nar TiCN 10-11 TiN 0.5 colum- 4.5 AlCN*¹ 0.5 AlN*¹ 0.5 6.0 48nar TiCN 10-12 TiN 0.5 TiCNO 2.0 colum- 6.0 TiBN 0.5 κ Al₂O₃ 1.5 AlCN*¹0.7 11.2 53 nar TiCN 10-13 colum- 2.0 HfCN 2.0 TiN 1.0 5.0 145 nar TiCN10-14 TiN 0.5 colum- 5.0 TiCNO 0.5 ZrO₂ 2.0 colum- 0.1 TiN 2.0 10.1 160nar nar TiCN TiCN 10-15 colum- 0.5 AlON*¹ 2.0 α Al₂O₃ 3.0 TiN 1.5 7.0136 nar TiCN 10-16 colum- 0.07 AlN*¹ 0.02 0.09 105 nar TiCN 10-17 colum-0.5 ZrCN 4.0 AlN*¹ 0.02 4.52 98 nar TiCN 10-18 TiN 0.5 colum- 3.0 TiCNO9.0 α Al₂O₃ 3.5 Al₂O₃— 5.0 AlCN*¹ 8.0 29.0 102 nar ZrO₂ TiCN 10-19colum- 4.0 TiBN 2.0 ZrO₂ 2.0 AlCN*¹ 7.0 15.0 95 nar TiCN 10-20 TiN 0.2colum- 0.8 ZrCN 4.0 AlON*² 1.3 6.3 148 nar TiCN 10-21 colum- 10.0 AlCN*¹4.0 14.0 94 nar TiCN

The surface-coated end mills with the coatings shown in Table 22 wereused to perform side milling under the conditions described below, andwear for a fixed cutting length (100 m) was measured. In this test, theflank face wear (microns) on the peripheral cutting edge was measured.Table 22 shows the results from the test as well.

End mill side milling

Workpiece: SUS304

Speed: V=144 m/min

Feed per cutting edge: ft=0.03 mm

Axial cutting depth: Ad=8 mm

Radial cutting depth: Rd=0.16 mm

Cutting oil: none

Cutting length: 100 m

As a result, it was found as shown in Table 22, that, compared to theother test samples, Test Samples 10-1-10-12, 10-16-10-19, 10-21, whichhad an aluminum nitride film containing a predetermined amount ofchlorine as the outermost layer and a columnar structure TiCN film innerlayer with an aspect ratio of at least 3 and a maximum index oforientation of TC(311), TC(220), or TC(422), provided superior lubricityand superior wear resistance.

Also, the results shown in Table 22 indicate that it is preferable forthe outermost layer to be at least 0.03 microns and for the total filmthickness to be at least 0.1 microns and no more than 24 microns.Furthermore, it can be seen that it is preferable for the outermostlayer to have no more than ½ the total thickness of the inner layer.

The end mills from the test sample 10-1-10-21 were all cut and thesurface roughness relative to a 5 micron reference length was measuredfor the area of the outermost layer near the ridge line of the cuttingedge of the peripheral cutting edge that contacts the workpiece. As aresult, it was found that Rmax was no more than 1.3 microns for all endmills except Test Sample 10-21, while the Rmax of Test Sample 10-21 was1.6 microns. For Test Sample 10-21, a #1500 diamond paste was used topolish the area of the outermost layer of the peripheral cutting edgenear the ridge line of the cutting edge that comes into contact with theworkpiece. When the method described above was used to measure surfaceroughness after polishing, Rmax was 0.61 microns. When side milling wasperformed under the same cutting conditions using the polished end mill,the flank face wear was 48 microns. This is believed to be caused by areduction in the cutting force resulting from less roughness at the areaof the outermost layer near the ridge line of the cutting edge thatcomes into contact with the workpiece.

TEST EXAMPLE 2-6′

Surface-coated end mills similar to those of Test Samples 10-1-10-21were prepared and cutting tests were performed under the cuttingconditions described below. Crater wear (width) on the peripheralcutting edge was then measured for a predetermined cutting length (50m).

The measurement of crater wear width was performed in a manner similarto that of the cutting test (Test Example 2-2′) that used thesurface-coated end mills from Test Samples 7-1-7-23.

Workpiece: S50C

Speed: V=120 m/min

Feed: f=0.05 mm/t

Cutting depth: Ad=10 mm Rd=0.6 mm

Cutting oil: none (air blower)

The results showed that Test Samples 10-1-10-12, 10-16-10-19, and 10-21had less crater wear compared to the other samples. For example, if thewear width of Test Sample 7-14 from Test Example 2-2′ is defined as 1,Test Samples 10-3, 10-6 had the values 0.39 and 0.42 respectively.

TEST EXAMPLE 2-7

Surface-coated end mills were prepared using the substrate describedbelow with a widely known PVD method being used to form a coating layerhaving a composition similar to that of Test Samples 10-2, 10-13 fromTable 22. For the end mill with a coating layer having a compositionsimilar to that of the Test Sample 10-2, the surface-coated end mill wasformed by adding chlorine to the outermost layer using ion implantationafter the coating layer was formed. Then, side milling was performedusing the same cutting conditions as Test Example 2-6. The coatinglayers were all formed at areas associated with cutting.

The test samples with the coating layer from Test Sample 10-2 all had achlorine content of 0.2 atomic percent on the outermost layer.

1 Brazed end mill substrate formed from cemented carbide correspondingto JIS Z20 (cutting section is cemented carbide)

2 Two-edge square end mill substrate formed from JIS-standard P20 cermet(10 mm diameter)

3 Brazed ball mill substrate formed from cubic boron nitride (SumitomoElectric Hardmetal Corp. Ltd., BN300) (cutting section is cubic boronnitride)

The results indicated that all the surface-coated end mills formed withthe coating layer from the Test Sample 10-2 provided superior lubricityand wear resistance. It was found that the tool life was at least twicethat of end mills formed with the conventional coating layer from theTest Sample 10-13.

THIRD EXAMPLE

The present invention will be described in further detail using drillsas an example.

TEST EXAMPLE 3-1

Solid drill substrates formed from cemented carbide corresponding to JISK10 (8 mm diameter) were prepared. Thermal CVD, which is a chemicalvapor deposition technique, was performed to form a coating layer on thesubstrate at the surface of the areas (body) associated with cuttingbased on the film forming conditions from Table 12. In this test, thefollowing layers were formed, starting from the substrate side: an innerlayer formed from TiN(0.5), TiCN(4), TiBN(0.5), κ-Al₂O₃(1) and anoutermost layer formed from AlN(1.5). The numbers in parenthesesindicate film thickness in microns. Film thickness was controlled bycontrolling the film forming time. Test samples in which the AlN film atthe outermost layer have different chlorine contents were prepared byvarying the film forming conditions as shown in Table 12. Table 23 showschlorine content at the outermost layer. Specifically, samples with morethan 0 and no more than 0.5 atomic percent of chlorine, samples withmore than 0.5 atomic percent of chlorine, and samples with no chlorinewere prepared. Chlorine content was varied as shown in Table 12 byvarying the proportion of hydrogen chloride (HCl) in the reaction gas.Also, depending on the amount of hydrogen chloride, the film formingpressure and the film forming temperature were varied as appropriate.Furthermore, the surface roughness at sites on the outermost layer nearthe ridge line of the cutting edge at areas that come into contact withthe workpiece were studied for test samples containing more than 0 andno more than 0.5 atomic percent of chlorine in the outermost layer.Observation of the tool cross-sections showed that the Rmax for areference length of 5 microns was no more than 1.3 microns for allsamples. More specifically, the Rmax was 0.6 microns for Test Sample11-2, for example. The chlorine content was measured using XPS (X-rayPhotoelectron Spectroscopy). Also, the Knoop hardness for each of thelayers in the test samples was studied, and it was found that in allcases the outermost AlN film was softer than the inner TiCN film layer.TABLE 23 Test Sample Outermost Chlorine content No. layer (atomicpercent) 11-1 AlN *¹ 0.03 11-2 AlN *¹ 0.18 11-3 AlN *¹ 0.48 11-4 AlN *²0 11-5 AlN *³ 0.98

Using the cutting conditions shown in Table 24, the cutting efficiencyof the surface-coated drills with outermost layers as shown in Table 23was observed. For cutting conditions 3, the number of holes bored untilthe tool broke was studied. For cutting conditions 4, the roundness ofthe holes was studied. The results of the tests are shown in Table 25.TABLE 24 Cutting conditions 3 Cutting conditions 4 Drill boring(through-hole) Drill boring (blind hole) Workpiece: SCM440 Workpiece:NAK80 Speed: V = 70 m/min Speed: V = 70 m/min Feed: f = 0.3 mm/rev.Feed: f = 0.25 mm/rev. Boring depth: 40 mm(L/D = 5) Boring depth: 40mm(L/D = 5) Cutting oil: None (external air blower) Cutting oil: watersoluble

TABLE 25 Cutting conditions 4 Test sample Cutting conditions 3 Roundnessof hole No. Number of holes before breakage entrance (microns) 11-1 Atleast 500 (no breaks) 3.5 11-2 At least 500 (no breaks) 2.1 11-3 Atleast 500 (no breaks) 2.8 11-4 285 13.8 11-5 182 15.9

Based on the results, in the Test Samples 11-1 through 11-3, which havealuminum nitride layers with more than 0 and not more than 0.5 atomicpercent of chlorine on the outermost layer as shown in Table 25, andinner layers with films having predetermined compositions, superior chipejection properties were provided and damage to the cutting section wasreduced, allowing good cuts over an extended period of time. Thissignificantly increased the number of cuts that could be made until thetool broke. This indicates that tool life was extended. For the TestSamples 11-1-11-3, it was found that the roundness of the bored holeswas superior and that high-precision cutting was possible. Furthermore,these Test Samples 11-1-11-3 provided superior welding resistance andpeeling of the coating layer and the like did not take place.

TEST EXAMPLE 3-2

Substrates similar to those from the cemented carbide drill substratesused in the Test Example 3-1 were prepared. Thermal CVD was performed onthe surface of the area associated with cutting, and coating layers wereformed under the film forming conditions (gas composition, pressure,temperature) shown in Table 12 in the same manner as the coating layersindicated in Table 16.

The surface-coated drills with the coatings shown in Table 16 were usedto perform boring operations under the conditions described below, andthe number of holes bored until the tool life was reached was measured.The end of tool life was defined to be when flank face wear at thecutting section at the end reached 0.3 microns or when further cuttingwas not possible due to tool breakage or the like. The results of thetests are shown in Table 26.

Drill boring (blind hole)

Workpiece: S50C

Speed: V=100 m/min

Feed: f=0.2 mm/rev.

Hole depth: 24 mm (L/D=3)

Cutting oil: air blower TABLE 26 Test Number of Sample Film holes boredNo. structure during tool life 12-1 7-1 3500 12-2 7-2 4500 12-3 7-3 550012-4 7-4 4000 12-5 7-5 5000 12-6 7-6 4000 12-7 7-7 3500 12-8 7-8 400012-9 7-9 4500 12-10 7-10 5500 12-11 7-11 3500 12-12 7-12 3500 12-13 7-13600 12-14 7-14 790 12-15 7-15 800 12-16 7-16 1260 12-17 7-17 1120 12-187-18 1310 12-19 7-19 1500 12-20 7-20 800 12-21 7-21 520 12-22 7-22 119012-23 7-23 1500

As a result, it was found as shown in Table 26 that, compared to theother test samples, the Test Samples 12-1-12-12, 12-16-12-19, 12-22, and12-23, which had an aluminum nitride film containing a predeterminedamount of chlorine as the outermost layer and films with predeterminedcompositions as the inner layers, provided superior lubricity andsuperior wear resistance.

Also, the results shown in Table 26 indicate that it is preferable forthe outermost layer to be at least 0.03 microns and for the total filmthickness to be at least 0.1 microns and no more than 24 microns.Furthermore, it can be seen that it is preferable for the outermostlayer to have no more than ½ the total thickness of the inner layer.

The drills from the test sample 12-1-12-23 were all cut and the surfaceroughness relative to a 5 micron reference length was measured for thearea of the outermost layer near the ridge line of the cutting edge ofthe peripheral cutting edge that comes into contact with the workpiece.As a result, it was found that Rmax was no more than 1.3 microns for alldrills except Test Sample 12-22, while the Rmax of Test Sample 12-22 was1.9 microns. For Test Sample 12-22, as in Test Sample 7-22, a #1500diamond paste was used to polish the area of the outermost layer of theperipheral cutting edge near the ridge line of the cutting edge thatcomes into contact with the workpiece. When the method described abovewas used to measure surface roughness after polishing, Rmax was 0.45microns. When boring was performed under the same cutting conditionsusing the polished drill, the number of operations performed was 4500.This is believed to be caused by a reduction in the cutting forceresulting from less roughness at the area of the outermost layer nearthe ridge line of the cutting edge that comes into contact with theworkpiece. When the surface roughness of the Test Sample 12-1 wasmeasured as described above, the Rmax was 0.78 microns, but when thecutting edge was polished in the same manner, the cut count afteranother boring operation was found to be significantly improved, at5000.

Furthermore, a coating film was formed on Test Sample 12-23 to make thefilm hardness of the inner layer lower than that of the outermost layer.Then, the hardnesses of the films forming the coating layers of TestSamples 12-1-12-20, 12-22, and 12-23 were measured. The film hardness ofthe outermost layer was lower than that of at least one film of theinner layer for all the drills, with the exception of Test Sample 12-23.With Test Sample 12-23, the film hardness of the outermost layer washigher than that of the inner layer. Based on this, it is believed thatthe cutting efficiency of Test Sample 12-23 was reduced compared to TestSamples 12-1-12-12.

TEST EXAMPLE 3-2′

Surface-coated drills similar to those of Test Samples 12-1-12-23 wereprepared and cutting tests were performed under the cutting conditionsdescribed below. Crater wear (width) was then measured for apredetermined number of holes (500 holes). Measurements were made on thewidths of crater wear near the center of the cutting section.Measurements were performed in a manner similar to those of Test Example2-2′.

Results were evaluated based on these measurements by comparing thedifferent test samples.

Workpiece: S50C (blind hole)

Speed: V=70 m/min

Feed: f=0.25 mm/rev.

Hole depth: 40 mm (L/D=5)

Cutting oil: mist (water soluble cutting fluid)

The results showed that Test Samples 12-1-12-12, 12-16-12-19, 12-22, and12-23 had less crater wear compared to the other samples. For example,if the wear width of the Test Sample 12-14 is defined as 1, Test Samples12-3, 12-9 had the values 0.32 and 0.38 respectively.

TEST EXAMPLE 3-2″

In the above test, dry cutting was performed. In this test, drillssimilar to those of the Test Samples 12-1-12-23 were prepared, andboring counts were measured as in the above test under the followingboring conditions: 40 mm boring depth (L/D=5); and cutting oil: insteadof using an air blower, wet cutting, and mist cutting were used. As aresult, it was found the Test Samples which had a aluminum nitride filmcontaining a predetermined amount of chlorine as the outermost layer andfilms with predetermined compositions as the inner layers providedsuperior lubricity, superior wear resistance, and longer tool life.

TEST EXAMPLE 3-3

Surface-coated drills were prepared using the substrate described belowwith a widely known PVD method being used to form a coating layer havinga composition similar to that of Test Samples 7-2, 7-13 from Table 16.For the drill with a coating layer having a composition similar to thatof Test Sample 7-2, the surface-coated drill was formed by addingchlorine to the outermost layer using ion implantation after the coatinglayer was formed. Then, boring (blind hole) was performed using the samecutting conditions (dry cutting) as Test Example 3-2. The coating layerswere all formed at areas associated with cutting.

Also, for the test samples on which the coating layer from Test Sample7-2 were formed, the chlorine content at the outermost layer was set to0.2 atomic percent.

1 High Speed Tool Steel Drill Substrate (Solid)

The results indicated that all the surface-coated drills formed with thecoating layer from the Test Sample 7-2 provided superior lubricity andwear resistance. It was found that the tool life was at least threetimes that of drills formed with the conventional coating layer from theTest Sample 7-13.

TEST EXAMPLE 3-4

Solid drill substrates formed from cemented carbide corresponding to JISK10 (8 mm diameter) were prepared. Thermal CVD, which is a chemicalvapor deposition technique, was performed to form a coating layer on thesubstrate at the surface of the areas (body) associated with cuttingbased on the film forming conditions from Table 17. In this test, thefollowing layers were formed, starting from the substrate side: an innerlayer formed from TiN(0.5), columnar structure TiCN(4), TiBN(0.5),κ-Al₂O₃(1) and an outermost layer formed from AlN(1.5). The numbers inparentheses indicate film thickness in microns. Film thickness wascontrolled by controlling the film forming time. In this test, the TiCNfilm was grown so that it has a columnar structure with an aspect ratioof 4.2 and so that the (311) plane has the maximum index of orientationTC. More specifically, the TiN film formation conditions (gascomposition, pressure, temperature) were set up so that the reaction gaswas CH₃CN, the temperature was 900 deg C., the pressure was 8 kPa, andthe surface roughness Rmax (5 microns reference length) of the TiN filmformed below the TiCN film was 0.1 microns. Test samples in which theAlN film at the outermost layer have different chlorine contents wereprepared by varying the film forming conditions as shown in Table 17.Table 27 shows chlorine content at the outermost layer. Specifically,samples with more than 0 and no more than 0.5 atomic percent ofchlorine, samples with more than 0.5 atomic percent of chlorine, andsamples with no chlorine in the outermost layer were prepared. Chlorinecontent was varied as shown in Table 17 by varying the proportion ofhydrogen chloride (HCl) in the reaction gas. Also, depending on theamount of hydrogen chloride, the film forming pressure and the filmforming temperature were varied as appropriate. Furthermore, the surfaceroughness at sites on the outermost layer near the ridge line of thecutting edge at areas that come into contact with the workpiece werestudied for test samples containing more than 0 and no more than 0.5atomic percent of chlorine in the outermost layer. Observation of thetool cross-sections showed that the Rmax for a reference length of 5microns was no more than 1.3 microns for all samples. More specifically,the Rmax was 0.6 microns for Test Sample 13-2, for example. The chlorinecontent was measured using XPS (X-ray Photoelectron Spectroscopy). TABLE27 Test sample Outermost Chlorine content No. layer (atomic %) 13-1 AlN*¹ 0.03 13-2 AlN *¹ 0.18 13-3 AlN *¹ 0.48 13-4 AlN *² 0 13-5 AlN *³ 0.98

Using the cutting conditions shown in Table 28, the cutting efficiencyof the surface-coated drills with outermost layers as shown in Table 27was observed. For cutting conditions III, the number of holes boreduntil the tool broke was studied. For cutting conditions IV, theroundness of the holes was studied. The results of the tests are shownin Table 29. TABLE 28 Cutting conditions III Cutting conditions IV Drillboring (through-hole) Drill boring (blind hole) Workpiece: SCM440Workpiece: NAK80 Speed: V = 70 m/min Speed: V = 70 m/min Feed: f = 0.3mm/rev. Feed: f = 0.25 mm/rev. Boring depth: 40 mm(L/D = 5) Boringdepth: 40 mm(L/D = 5) Cutting oil: none (external air blower) Cuttingoil: water soluble

TABLE 29 Cutting conditions III Cutting conditions IV Test Sample Numberof holes before Roundness of hole No. breakage entrance (microns) 13-1At least 500 (no breaks) 3.8 13-2 At least 500 (no breaks) 1.9 13-3 Atleast 500 (no breaks) 3.1 13-4 312 15.3 13-5 250 12.1

Based on the results, in Test Samples 13-1 through 13-3, which havealuminum nitride layers with more than 0 and not more than 0.5 atomicpercent of chlorine on the outermost layer as shown in Table 29, andpredetermined inner TiCN film layers, superior chip ejection propertieswere provided and damage to the cutting section was reduced, allowinggood cuts over an extended period of time. This significantly increasedthe number of cuts that could be made until the tool broke. Thisindicates that tool life was extended. For Test Samples 13-1-13-3, itwas found that the roundness of the bored holes was superior and thathigh-precision cutting was possible. Furthermore, these Test Samples13-1-13-3 provided superior welding resistance and peeling of thecoating layer and the like did not take place.

TEST EXAMPLE 3-5

Substrates similar to those from the cemented carbide drill substratesused in Test Example 3-4 were prepared. Thermal CVD was performed on thesurface of the area associated with cutting, and coating layers wereformed under the film forming conditions (gas composition, pressure,temperature) shown in Table 17. In this test, the following layers wereformed, starting from the substrate side: TiN(0.5), columnar structureTiCN(4) or granular structure TiCN(4), TiBN(0.5), Al₂O₃—ZrO₂(1); and anoutermost layer formed from AlN*¹(1.5) (similar to Test Sample 8-3 fromTable 18). The numbers in parentheses indicate film thickness inmicrons. Film thickness was controlled by controlling the film formingtime. In this test, the aspect ratio and the face with the maximum indexof orientation of the columnar structure TiCN film are varied, as shownin Table 17, by varying the film forming pressure and temperature aswell as by varying the surface roughness and gas conditions for the TiNfilm formed below the TiCN film. More specifically, the aspect ratio ofthe TiCN film was set to at least 3 by using CH₃CN as the reaction gas,with the gas temperature set to 920 deg C. and the pressure set to 6 kPaand the CH₃CN reaction gas being introduced gradually. Also, if the TiCNfilm maximum index of orientation is to be TC(422), for example, thesurface roughness Rmax (reference length) of the substrate is set to0.09 microns and the TiCN film is formed while adjusting the aspectratio outward from the substrate (away from the substrate). Furthermore,for all the test samples, the surface of the outermost layer waspolished after forming the outermost layer so that the section of theoutermost layer around the ridge line of the cutting edge that comesinto contact with the workpiece had a surface roughness Rmax of 0.4microns for 5 microns reference length when measured by observing toolcross-sections. Table 30 shows TiCN film structure, aspect ratio, andthe face with the maximum index of orientation TC. TABLE 30 Inner layerTiCN film Test Face with Sample Aspect maximum Number of holes bored No.Structure ratio TC during tool life 14-1 Columnar 5.1 311 800 14-2Columnar 7.0 422 920 14-3 Columnar 3.2 220 900 14-4 Columnar 2.1 220 25014-5 Columnar 4.0 420 210 14-6 Granular — 311 330

The surface-coated drills with the TiCN films shown in Table 30 formingan inner layer were used to perform boring operations under theconditions described below, and the number of holes bored until the toollife was reached was measured. The end of tool life was defined to bewhen flank face wear at the cutting section at the end reached 0.3microns or when further cutting was not possible due to tool breakage orthe like. Table 30 shows the results from the test as well.

Drill Boring (Through-hole)

Workpiece: S50C

Speed: V=80 m/min

Feed: f=0.2 mm/rev.

Hole depth: 40 mm (L/D=5)

Cutting oil: mist (water soluble cutting fluid)

The results show that with a TiCN film as an inner layer as in Table 30,a columnar structure provides superior wear resistance. Morespecifically, with Test Samples 14-1-14-3, which are formed withcolumnar structure TiCN film at the inner layer with an aspect ratio ofat least 3 and a maximum index of orientation of TC(311), TC(220), orTC(422), wear resistance and breakage resistance are especially superiorand tool life is longer. The longer tool life is believed to be becauseof the superior lubricity of the outermost layer and the use of apredetermined TiCN film with superior wear resistance as the innerlayer.

TEST EXAMPLE 3-6

Substrates similar to those from the cemented carbide drill substratesused in Test Example 3-4 were prepared. Thermal CVD was performed on thesurface of the area associated with cutting, and coating layers wereformed under the film forming conditions (gas composition, pressure,temperature) shown in Table 17 in the same manner as the coating layersshown in Table 22. In this test, as in the Test Example 2-6, the filmforming conditions were controlled so that columnar structure TiCN filmshad an aspect ratio of at least 3 and the maximum index of orientationwas TC(311), TC(220), or TC(422).

The surface-coated drills with the coatings shown in Table 22 were usedto perform boring operations under the conditions described below, andthe number of holes bored until the tool life was reached was measured.The end of tool life was defined to be when flank face wear at thecutting section at the end reached 0.3 microns or when further cuttingwas not possible due to tool breakage or the like. The results of thetests are shown in Table 31.

Drill boring (blind hole)

Workpiece: S50C

Speed: V=120 m/min

Feed: f=0.2 mm/rev.

Hole depth: 24 mm (L/D=3)

Cutting oil: air blower TABLE 31 Test Number of Sample Film holes boredNo. structure during tool life 15-1 10-1 4000 15-2 10-2 4500 15-3 10-35000 15-4 10-4 4500 15-5 10-5 5500 15-6 10-6 4500 15-7 10-7 3500 15-810-8 4000 15-9 10-9 4000 15-10 10-10 5500 15-11 10-11 4000 15-12 10-124500 15-13 10-13 820 15-14 10-14 600 15-15 10-15 800 15-16 10-16 105015-17 10-17 1420 15-18 10-18 1330 15-19 10-19 1200 15-20 10-20 510 15-2110-21 1010

As a result, it was found as shown in Table 31 that Test Samples15-1-15-12, 15-16-15-19, 15-21, which had an aluminum nitride filmcontaining a predetermined amount of chlorine as the outermost layer anda columnar structure TiCN film inner layer with an aspect ratio of atleast 3 and a maximum index of orientation of TC(311), TC(220), orTC(422), provided superior lubricity and superior wear resistancecompared to Test Samples 15-13-15-15, 15-20, which correspond toconventional technologies.

Also, the results shown in Table 31 indicate that it is preferable forthe outermost layer to be at least 0.03 microns and for the total filmthickness to be at least 0.1 microns and no more than 24 microns.Furthermore, it can be seen that it is preferable for the outermostlayer to have no more than ½ the total thickness of the inner layer.

The drills from test sample 15-1-15-21 were all cut and the surfaceroughness relative to a 5 micron reference length was measured for thearea of the outermost layer near the ridge line of the cutting edge ofthe peripheral cutting edge that comes into contact with the workpiece.As a result, it was found that Rmax was no more than 1.3 microns for alldrills except the Test Sample 15-21, while the Rmax of Test Sample 15-21was 2.0 microns. For Test Sample 15-21, as in Test Sample 10-21, a #1500diamond paste was used to polish the area of the outermost layer of theperipheral cutting edge near the ridge line of the cutting edge thatcomes into contact with the workpiece. When the method described abovewas used to measure surface roughness after polishing, Rmax was 0.52microns. When boring was performed under the same cutting conditionsusing the polished drill, the number of operations performed was 4000.This is believed to be caused by a reduction in the cutting forceresulting from less roughness at the area of the outermost layer nearthe ridge line of the cutting edge that comes into contact with theworkpiece.

TEST EXAMPLE 3-6′

Surface-coated drills similar to those of Test Samples 15-1-15-21 wereprepared and cutting tests were performed under the cutting conditionsdescribed below. Crater wear (width) was then measured for apredetermined number of holes (500 holes) near the center of the cuttingsection.

The measurement of crater wear width was performed in a manner similarto that of the cutting test (Test Example 3-2′) that used thesurface-coated drills from Test Samples 12-1-12-23.

Workpiece: S50C (blind hole)

Speed: V=100 m/min

Feed: f=0.25 mm/rev.

Hole depth: 40 mm (L/D=5)

Cutting oil: mist (water soluble cutting fluid)

The results showed that Test Samples 15-1-15-12, 15-16-15-19, and 15-21had less crater wear compared to the other samples. For example, if thewear width of Test Sample 12-14 from Test Example 3-2′ is defined as 1,Test Samples 15-3, 15-9 had the values 0.29 and 0.35 respectively.

TEST EXAMPLE 3-6″

In the above test, dry cutting was performed. In this test, drillssimilar to those of Test Samples 15-1-15-21 were prepared, and boringcounts were measured as in the above test under the following boringconditions: 40 mm boring depth (L/D=5); and cutting oil: wet cutting,mist cutting instead of using an air blower. As a result, it was foundthat the test samples, which had an aluminum nitride film containing apredetermined amount of chlorine as the outermost layer and a columnarstructure TiCN film inner layer with an aspect ratio of at least 3 and amaximum index of orientation of TC(311), TC(220), or TC(422), providedsuperior lubricity and superior wear resistance as well as long toollife.

TEST EXAMPLE 3-7

Surface-coated drills were prepared using the substrate described belowwith a widely known PVD method being used to form a coating layer havinga composition similar to that of Test Samples 10-2, 10-13 from Table 22.For the drill with a coating layer having a composition similar to thatof Test Sample 10-2, the surface-coated drill was formed by addingchlorine to the outermost layer using ion implantation after the coatinglayer was formed. Then, boring (blind hole) was performed using the samecutting conditions (dry cutting) as Test Example 3-6. The coating layerswere all formed at areas associated with cutting.

Also, for the test samples on which the coating layer from the TestSample 10-2 were formed, the chlorine content at the outermost layer wasset to 0.2 atomic percent.

1. High Speed Tool Steel Drill Substrate (Solid)

The results indicated that all the surface-coated drills formed with thecoating layer from the Test Sample 10-2 provided superior lubricity andwear resistance. It was found that the tool life was at least threetimes that of drills formed with the conventional coating layer from theTest Sample 10-13.

The surface-coated cutting tool of the present invention is suited forcutting under harsh conditions, e.g., cutting involving hightemperatures for the cutting edge such as dry cutting, mist cutting, andintermittent cutting, boring, and cutting of workpieces that tend toweld easily.

Also, the surface-coated cutting tool of the present invention is suitedfor cutting steel and the like under conditions that tend to lead towelding.

1. A surface-coated cutting tool comprising: a coating layer on asubstrate surface having: an inner layer formed on a substrate; and anoutermost layer formed over said inner layer; wherein said inner layeris formed from a compound formed from a first element and a secondelement, said first element being at least one element selected from agroup consisting of a periodic table group IVa, Va, VIa metal, Al, Si,and B, and said second element being at least one element selected froma group consisting of B, C, N, and O, except, in said inner layer, afilm formed solely from B is excluded; wherein said outermost layer isformed from aluminum nitride or aluminum carbonitride, said outermostlayer containing more than 0 and no more than 0.5 atomic percentchlorine.
 2. A surface-coated cutting tool according to claim 1 whereinsaid outermost layer further includes oxygen.
 3. A surface-coatedcutting tool according to claim 1 wherein said inner layer includes afilm formed from a compound containing Ti.
 4. A surface-coated cuttingtool according to claim 3 wherein said inner layer includes a filmformed from TiCN having a columnar structure.
 5. A surface-coatedcutting tool according to claim 4 wherein said film formed from TiCN hasa columnar structure with an aspect ratio of at least 3, where an indexof orientation TC(220), TC(311), or TC(422) of a crystal face (220),crystal face (311), or crystal face (422) respectively is a maximumindex of orientation.
 6. A surface-coated cutting tool according toclaim 1 wherein said outermost layer is formed with a film thicknessthat is no more than ½ a total film thickness of said inner layer.
 7. Asurface-coated cutting tool according to claim 1 wherein a film hardnessof said outermost layer is lower than a hardness of at least one filmforming said inner layer.
 8. A surface-coated cutting tool according toclaim 1 wherein a surface roughness of a section of said outermost layernear a ridge line of a cutting edge has an Rmax relative to a 5 micronreference length of no more than 1.3 microns, where roughness ismeasured by observing a cross-section of said cutting tool.
 9. Asurface-coated cutting tool according to claim 1 wherein said substrateis formed from a WC-based cemented carbide, cermet, high-speed steel,ceramic, a cubic boron nitride sintered body, or a silicon nitridesintered body.
 10. A surface-coated cutting tool according to claim 1wherein said surface-coated cutting tool is a throw-away insert, adrill, or an end mill.
 11. A surface-coated cutting tool according toclaim 1 wherein: said surface-coated cutting tool is a throw-awayinsert; and said outermost layer has a film thickness of at least 0.03microns and no more than 10 microns, and said coating layer has a totalfilm thickness of at least 0.1 microns and no more than 30 microns. 12.A surface-coated cutting tool according to claim 1 wherein: saidsurface-coated cutting tool is a drill or an end mill; and saidoutermost layer has a film thickness of at least 0.03 microns and nomore than 8 microns, and said coating layer has a total film thicknessof at least 0.1 microns and no more than 24 microns.